A hyaluronic acid derivative in which a non-steroidal anti-inflammatory drug is bound to hyaluronic acid through a covalent bond, wherein a partial structure of a hyaluronic acid disaccharide unit into which the anti-inflammatory drug is introduced is represented by the following formula: Y-CO-NH-R 1 -(O-R 2) n wherein Y-CO- represents the glucuronic acid residue of the hyaluronic acid disaccharide unit; R 2 represents a hydrogen atom or a non-steroidal anti-inflammatory drug residue having a carboxyl group and at least one R 2 is a non-steroidal anti-inflammatory drug residue; -HN-R 1 -(O-) n represents a spacer residue of a spacer compound represented by H 2 N-R 1 - n having n hydroxyl groups; R 1 represents a linear or branched hydrocarbon group having from 2 to 12 carbon atoms which may have a substituent; a hydroxyl group in the spacer compound forms an ester bond with a carboxyl group in the non-steroidal anti-inflammatory drug residue; -CO-NH- represents an amide bond of a carboxyl group in a glucuronic acid as a constituting saccharide of the hyaluronic acid with an amino group in the spacer compound; and n is an integer of from 1 to 3; wherein the carbonyl group in a hyaluronic acid residue constituting the hyaluronic acid derivative is present as an amide bond participating in the binding with the spacer-binding anti-inflammatory drug residue or as a free carboxyl group not participating therein; and wherein the hyaluronic acid derivative has a degree of substitution of the non-steroidal anti-inflammatory drug of from 5 to 50 mol% per repeating disaccharide unit of hyaluronic acid; and wherein the non-steroidal anti-inflammatory drug is a compound represented by the following formula: wherein R 3 represents a substituent selected from the group consisting of a lower alkyl group, a lower alkoxyl group and a hydrogen atom; R 4, R 5 and R 6 each independently represent a substituent selected from the group consisting of a lower alkyl group, a lower alkoxyl group, a hydroxyl group, a halogen atom and a hydrogen atom; and each X is the same or different and each represents a substituent selected from the group consisting of a lower alkyl group, a trifluoromethyl group and a halogen atom, wherein at least one of X is a halogen atom, and wherein a lower alkyl group and a lower alkoxyl group is a group having from 1 to 12 carbon atoms which are allowed to be branched. wherein Y-CO- represents the glucuronic acid residue of the hyaluronic acid disaccharide unit; R 2 represents a hydrogen atom or a non-steroidal anti-inflammatory drug residue having a carboxyl group and at least one R 2 is a non-steroidal anti-inflammatory drug residue; -HN-R 1 -(O-) n represents a spacer residue of a spacer compound represented by H 2 N-R 1 - n having n hydroxyl groups; R 1 represents a linear or branched hydrocarbon group having from 2 to 12 carbon atoms which may have a substituent; a hydroxyl group in the spacer compound forms an ester bond with a carboxyl group in the non-steroidal anti-inflammatory drug residue; -CO-NH- represents an amide bond of a carboxyl group in a glucuronic acid as a constituting saccharide of the hyaluronic acid with an amino group in the spacer compound; and n is an integer of from 1 to 3; wherein the carbonyl group in a hyaluronic acid residue constituting the hyaluronic acid derivative is present as an amide bond participating in the binding with the spacer-binding anti-inflammatory drug residue or as a free carboxyl group not participating therein; and wherein the hyaluronic acid derivative has a degree of substitution of the non-steroidal anti-inflammatory drug of from 5 to 50 mol% per repeating disaccharide unit of hyaluronic acid; and wherein the non-steroidal anti-inflammatory drug is a compound represented by the following formula: wherein R 3 represents a substituent selected from the group consisting of a lower alkyl group, a lower alkoxyl group and a hydrogen atom; R 4, R 5 and R 6 each independently represent a substituent selected from the group consisting of a lower alkyl group, a lower alkoxyl group, a hydroxyl group, a halogen atom and a hydrogen atom; and each X is the same or different and each represents a substituent selected from the group consisting of a lower alkyl group, a trifluoromethyl group and a halogen atom, wherein at least one of X is a halogen atom, and wherein a lower alkyl group and a lower alkoxyl group is a group having from 1 to 12 carbon atoms which are allowed to be branched.