A new species of Arcidae is described and named as Arca taiwanensis. This new species is discovered from the shallow seas of eastern Taiwan. The unique features of the new species include: (1) Shell is small. (2) Shell is flat and subtriangular in side view. (3) Shell is very inflated and ovate in dorsal view. (4) It seems that it lacks umbo. (5) Shell outer surface is poor in sculpture. (6) Digamental area is very wide. (7) Byssal gape is wide and elongated. The holotype is deposited in National Taiwan Museum in Taipei. Some Taiwanese species of genus Arca are illustrated for comparison.