Psychological Refractory Period (PRP) is the delay in the response to the second of two closely spaced stimuli. This study was examined to find out the effects of inter-stimulus intervals and number of alternatives on PRP. Subjects were 5 female students who participated in experiment voluntarily. Experimental task was double-stimulus task which first task was button pressing and second task was target aiming. Results showed that inter-stimulus interval influences on PRP, and number of alternatives does influence on PRP.