A resin composition comprising an ethylene-vinyl alcohol copolymer, a hydrate-forming metal salt, and a polyamide-based resin, wherein the polyamide-based resin includes an aromatic polyamide-based resin whose main chain includes a structural unit containing an aromatic ring and aliphatic polyamide-based resin whose main chain includes an aliphatic hydrocarbon containing 5 or more carbon atoms, wherein a weight ratio of the aromatic polyamide-based resin to the aliphatic polyamide-based resin, /, is from 55/45 to 99/1, wherein the aromatic polyamide-based resin is a copolymer type polyamide which contains a unit derived from an aromatic-containing diamine, and a unit derived from a linear aliphatic dicarboxylic acid having 4 or less carbon atoms in the aliphatic hydrocarbon chain, wherein the aromatic-containing diamine is ortho-xylylenediamine, meta-xylylenediamine or para-xylylenediamine, and wherein the hydrate-forming metal salt satisfies at least one water absorption property,, or: water absorption property: a ratio (X 5 /Y) is 0.2 or more, wherein X 5 is an amount of water absorption per 100 g of hydrate-forming metal salt when the hydrate-forming metal salt is placed for 5 days under the condition of 40 °C and 90 % relative humidity; wherein Y is an amount of water which is able to be trapped in 100 g of hydrate-forming metal salt with no water of crystallization, and wherein Y is calculated by the formula Y (g) = [(hydration number of hydrate in a state of maximum hydration x 18)/(molecular weight of anhydrate) x 100]; water absorption property: an amount of water absorbed per 100g of the hydrate-forming metal salt while the hydrate-forming metal salt is placed for 24 hours under the condition of 40 °C and 90 % relative humidity, is 10 g or more; water absorption property: a local maximum point exists in an amount of water absorption when the hydrate-forming metal salt is placed under the condition of 40 °C and 90% relative humidity, wherein the local maximum point is a turning point for changing to decreasing tendency in the amount of water absorption while being placed for 6 days under the condition of 40 °C and 90 % relative humidity. wherein the polyamide-based resin includes an aromatic polyamide-based resin whose main chain includes a structural unit containing an aromatic ring and aliphatic polyamide-based resin whose main chain includes an aliphatic hydrocarbon containing 5 or more carbon atoms, wherein a weight ratio of the aromatic polyamide-based resin to the aliphatic polyamide-based resin, /, is from 55/45 to 99/1, wherein the aromatic polyamide-based resin is a copolymer type polyamide which contains a unit derived from an aromatic-containing diamine, and a unit derived from a linear aliphatic dicarboxylic acid having 4 or less carbon atoms in the aliphatic hydrocarbon chain, wherein the aromatic-containing diamine is ortho-xylylenediamine, meta-xylylenediamine or para-xylylenediamine, and wherein the hydrate-forming metal salt satisfies at least one water absorption property,, or: water absorption property: a ratio (X 5 /Y) is 0.2 or more, wherein X 5 is an amount of water absorption per 100 g of hydrate-forming metal salt when the hydrate-forming metal salt is placed for 5 days under the condition of 40 °C and 90 % relative humidity; wherein Y is an amount of water which is able to be trapped in 100 g of hydrate-forming metal salt with no water of crystallization, and wherein Y is calculated by the formula Y (g) = [(hydration number of hydrate in a state of maximum hydration x 18)/(molecular weight of anhydrate) x 100]; water absorption property: an amount of water absorbed per 100g of the hydrate-forming metal salt while the hydrate-forming metal salt is placed for 24 hours under the condition of 40 °C and 90 % relative humidity, is 10 g or more; water absorption property: a local maximum point exists in an amount of water absorption when the hydrate-forming metal salt is placed under the condition of 40 °C and 90% relative humidity, wherein the local maximum point is a turning point for changing to decreasing tendency in the amount of water absorption while being placed for 6 days under the condition of 40 °C and 90 % relative humidity. water absorption property: a ratio (X 5 /Y) is 0.2 or more, wherein X 5 is an amount of water absorption per 100 g of hydrate-forming metal salt when the hydrate-forming metal salt is placed for 5 days under the condition of 40 °C and 90 % relative humidity; wherein Y is an amount of water which is able to be trapped in 100 g of hydrate-forming metal salt with no water of crystallization, and wherein Y is calculated by the formula Y (g) = [(hydration number of hydrate in a state of maximum hydration x 18)/(molecular weight of anhydrate) x 100]; water absorption property: an amount of water absorbed per 100g of the hydrate-forming metal salt while the hydrate-forming metal salt is placed for 24 hours under the condition of 40 °C and 90 % relative humidity, is 10 g or more; water absorption property: a local maximum point exists in an amount of water absorption when the hydrate-forming metal salt is placed under the condition of 40 °C and 90% relative humidity, wherein the local maximum point is a turning point for changing to decreasing tendency in the amount of water absorption while being placed for 6 days under the condition of 40 °C and 90 % relative humidity.