To provide an acrylic fiber and a pile fabric having improved discharge printing properties of fibers especially subjected to fiber dyeing at a high density without deteriorating the quality and touch feeling.

The acrylic synthetic fiber is obtained from an acrylic copolymer having 35-55 wt.% content of acrylonitrile, 44.3-64.3 wt.% content of a halogen-containing monomer and 0.7 wt.% content of a sulfonic acid group-containing monomer and having ≥5.6×104 to ≤8.5×104 weight-average molecular weight. The pile fabric comprises ≥10 wt.% of the acrylic synthetic fiber in which ≤0.80 relaxation ratio is imparted by wet heat treatment.