In order to construct a constitutive equation for polymeric solids, cyclic combined tension-torsion tests were performed using polyoximethylene (POM) at strain paths such as proportional, cruciform, rhombus and circular ones to investigate the effect of strain history on the stress-strain curve. It was shown that : (1) cyclic softening occurs for all strain paths tested here, (2) stress response for all strain paths is influenced by the hydrostatic stress component, (3) stress softening for the circular strain path greatly depends on the previous strain path and (4) stress relaxation after several stroain cycles strongly depends on the direction of the present strain.