Unconditioned stimulus (UCS) inflation procedure was a method that UCS intensity was gradually inflated, and UCS deflation procedure was a method that UCS intensity was gradually deflated. This study was aimed to examine the effect of UCS inflation and UCS deflation procedures on the conditioned response (CR) strength by two differential conditioning experiments (experiment 1 and 2). In both experiments, fifteen undergraduate volunteers served as subjects. They participated in both experiment and control conditions. Both conditions were consisted of four sessions, those were pre-test, conditioning, UCS intensity operation and test. The difference of experiment and control conditions was the operation of UCS intensity. UCSs of varied intensity were used in experiment conditions, where as those of same intensity for conditioning sessions were used in control conditions. The main results were follows. (1) In experiment 1 with UCS inflation procedure, differential CRs were found during test session for experiment condition, where as those were not found for control condition. (2) In experiment 2 with UCS deflation procedure, differential CRs were not found for experiment condition, where as those were found for control condition. These results suggested that the CR strength were influenced by UCS intensity operations.