To provide a yarn for a synthetic fiber brush and a synthetic fiber brush, such that dirt can be removed by the brush alone or with water or water mixed with a detergent, while reducing limitations imposed by the shape, condition, narrowness, and harness of a dirty object to be washed, materials constituting the dirt, the detergent used, a washing liquid, etc.

Two to four crimped multifilaments with, 1,000 to 4,000 denier, whose component unit is a deformed-cross-section yarn with a single-yarn denier of 20 to 50 and with a deformation factor of 0.9 or less as defined by the formula (1): deformation factor = (radius of inscribed circle/radius of circumscribed circle) on its cross section, are twisted together to form a yarn with a total denier of 4,000 to 8,000.