A catalyst for producing acrylic acid from propane and/or acrolein by gas-phase catalytic oxidation with molecular oxygen-containing gas, comprising a catalytic active component, wherein: the catalyst is prepared by a method comprising the step of adding an aqueous solution containing the component B in the following formula to an aqueous solution containing molybdenum and vanadium over a period of 30 seconds to 10 minutes; the catalytic active component has a composition expressed by the following formula; and the catalytic active component contains a crystalline part showing a peak at 2θ = 22.2 ± 0.5°, measured by an X-ray diffraction analysis with Cu-Kα radiation, and has a crystallinity T of 5% or more and 20% or less in the 2θ range of 5° to 90°, measured by an X-ray diffraction analysis with Cu-Kα radiation; and a crystallinity ratio R expressed by the following formula is in the range of 0.06 or more and 0.30 or less R = M / T wherein M represents a crystallinity of the peak at 2θ = 22.2 ± 0.5° in the catalytic active component, measured by the X-ray diffraction analysis with Cu-Kα radiation, MO a V b A c B d C e D f O z wherein Mo is molybdenum; V is vanadium; A represents niobium and/or tungsten; B represents at least one kind of element selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc and bismuth; C represents at least one kind of element selected from the group consisting of tin, antimony and tellurium; D represents at least one kind of element selected from the group consisting of titanium, aluminum, silicon and zirconium; O is oxygen; a, b, c, d, e, f and z mean atomic ratios of Mo, V, A, B, C, D and O, respectively, and meet inequalities: a = 12, 1 ≤ b ≤ 14, 0 ≤ c ≤ 12, 0 ≤ d ≤ 10, 0 ≤ e ≤ 6 and 0 ≤ f ≤ 40, respectively; and z is a numeral value determined by oxidation states of respective elements. the catalyst is prepared by a method comprising the step of adding an aqueous solution containing the component B in the following formula to an aqueous solution containing molybdenum and vanadium over a period of 30 seconds to 10 minutes; the catalytic active component has a composition expressed by the following formula; and the catalytic active component contains a crystalline part showing a peak at 2θ = 22.2 ± 0.5°, measured by an X-ray diffraction analysis with Cu-Kα radiation, and has a crystallinity T of 5% or more and 20% or less in the 2θ range of 5° to 90°, measured by an X-ray diffraction analysis with Cu-Kα radiation; and a crystallinity ratio R expressed by the following formula is in the range of 0.06 or more and 0.30 or less R = M / T wherein M represents a crystallinity of the peak at 2θ = 22.2 ± 0.5° in the catalytic active component, measured by the X-ray diffraction analysis with Cu-Kα radiation, MO a V b A c B d C e D f O z wherein Mo is molybdenum; V is vanadium; A represents niobium and/or tungsten; B represents at least one kind of element selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc and bismuth; C represents at least one kind of element selected from the group consisting of tin, antimony and tellurium; D represents at least one kind of element selected from the group consisting of titanium, aluminum, silicon and zirconium; O is oxygen; a, b, c, d, e, f and z mean atomic ratios of Mo, V, A, B, C, D and O, respectively, and meet inequalities: a = 12, 1 ≤ b ≤ 14, 0 ≤ c ≤ 12, 0 ≤ d ≤ 10, 0 ≤ e ≤ 6 and 0 ≤ f ≤ 40, respectively; and z is a numeral value determined by oxidation states of respective elements. wherein M represents a crystallinity of the peak at 2θ = 22.2 ± 0.5° in the catalytic active component, measured by the X-ray diffraction analysis with Cu-Kα radiation, MO a V b A c B d C e D f O z wherein Mo is molybdenum; V is vanadium; A represents niobium and/or tungsten; B represents at least one kind of element selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc and bismuth; C represents at least one kind of element selected from the group consisting of tin, antimony and tellurium; D represents at least one kind of element selected from the group consisting of titanium, aluminum, silicon and zirconium; O is oxygen; a, b, c, d, e, f and z mean atomic ratios of Mo, V, A, B, C, D and O, respectively, and meet inequalities: a = 12, 1 ≤ b ≤ 14, 0 ≤ c ≤ 12, 0 ≤ d ≤ 10, 0 ≤ e ≤ 6 and 0 ≤ f ≤ 40, respectively; and z is a numeral value determined by oxidation states of respective elements.