The CaSO4 whisker／polyurethane elastomer composites with high strength and high toughness are fabricated．The CaSO4 whisker reinforcing and toughening mechanisms for polyurethane elastomer are stMied．The observation of the fracture surface by SEM and TEM shows that CaSO4 whisker reinforcing mechanism for polyurethane elastomer is mainly load transfering

while its toughening mechanism involves crack deflection and whisker pullout．The effects of dispereity of CaSO4 whisker and the interfacial bonding state on reinforcement and toughness are discussed．The re8ults indicate that compooites with 5％～10％ CaSO4 whisker exhibit the best mechanical properties among the materials tested．Good bonding interface is formed between whisker and matrix after the surface of CaSO4 whisker being treated by silane coupling agent(KH-550)．Better interracial bonding state contributes to strength and toughness being fairly improved．