The present study analyzed characteristics of polyurethane (PU) softballs under variable relative humidity (RR) conditions. Inorder to understand the PU softball spheroid characteristics， testing of circumference，weight，coefficient of restitution (COR) and compression values (CV) under six variable humidity environmental conditions were conducted. Experimental results indicated that when PU softball spheroids were under varied humidity environmental conditions， circumference and weight did not significantly vary. But COR and CV of PU softball spheroids were reduced企om 3.3% to 23.16% depending on RR% conditions. Results from this study indicate that environmental conditions affected PU softball spheroids.