Crosslink structures of poly(urethane-urea) elastomers were studied by analyzing the compressive stress-strain properties of swollen rubber in different solvents. The network chain density measured in chloroform represented both chemical and physical bonds whereas the network crosslink density measured in tetrahydrofuran represented chemical crosslinking. Using the difference of the two solvents, the quantity of each network chain density can be evaluated. This approach enables us to discuss the contribution enables us to discuss the contribution of each bond to the properties of poly(urethane-urea) elastomers. The elongation at break of the polymers was expressed as a function of the physical network crosslink density. It was found that the physical bonds are destroyed on stretching a rubber while the chemical bonds remain constant. The chemical crosslinks are reduced by heat treatment in a manner that can be expressed by a first order reaction.