The present invention provides: an acrylic fiber having a fineness of 0.5 to 3.5 dtex and having excellent gloss, pilling resistance, and texture; a method for producing said acrylic fiber; and a spun yarn and a knitted fabric containing said acrylic fiber. Provided is an acrylic fiber having a filament fineness of 0.5 to 3.5 dtex, wherein the product K of the value of knot strength (cN/dtex) and the value of knot elongation (%) is from 8 to 30 inclusive, and the number of recesses having a depth of 0.1 µm or greater is 10 or fewer. In this method for producing said acrylic fiber, an acrylonitrile-based copolymer containing 92 to 96.8 mass% of an acrylonitrile unit, 2 to 6 mass% of a vinyl-based monomer unit, and 0.2 to 2.0 mass% of a sulfonic acid group-containing vinyl monomer unit is dissolved in an organic solvent, to prepare a spinning dope. A coagulated fiber bundle is formed by discharging the spinning dope from discharge holes into a coagulation bath having a solvent concentration of 40 to 60 mass% and a temperature of 35 to 50 °C. The coagulated fiber bundle is drawn in hot water at a draw ratio of 2 to 3.8 times, an oil agent is applied, the fiber bundle is dried, and then the fiber bundle is drawn under dry heat at a draw ratio of 1.2 to 3 times.
The product S of said draw ratio in hot water and said draw ratio under dry heat is from 4 to 6 times. Further, the fiber bundle is subjected to a thermal relaxation treatment.