A series of PVC/NBR blends with varying acrylonitrile (AN) content in the NBR has been studied in uniaxial tension creep tests. The tests have been carried out at 21.5 ± 0.5°C covering creep times from 10 to 1000 sec. NBR with low AN content, having poor compatibility with PVC, gives the blends with higher compliance and increased time dependence of the compliance. A higher AN content in the NBR gives the blends with the opposite properties when the NBR is added in small amounts. NBR with 40 wt‐% AN is found to act as an antiplasticizer giving minimal creep compliance when 7 wt‐% NBR is added. The antiplasticization reveals a considerably increased stress level at which the transition from approximatively linear to marked nonlinear viscoelasticity occurs and a decreased stress dependence of the creep compliance in the nonlinear viscoelastic range. Since the antiplasticization is also associated with a suppression of the β‐transition mechanism, the results provide a demonstration of the importance of β‐mechanism in the stress activated processes responsible for the appearance of nonlinear viscoelasticity in solid polymers.