The purpose of this study was to analyse the effect of residual primer on adhesion of two-step self-etch adhesive. For this, the microtensile bond strength (μTBS) and degree of conversion using a Fourier transform infrared specterometer (FTIR) were measured. Denting bonding system used in this study was Cleafil SE bond (Kuraray Medical Inc., Tokyo, Japan). In the control group, residual primer was not used. For four experimental groups, primer solution was added 0.5 ㎕ increments from 0.5 ㎕ to 2.0 ㎕ in adhesive resin. Data were analyzed by one-way ANOVA and Scheffe test at 95% significance level. Group 4 showed significantly lower μTBS than other groups (p<0.05). Group 2, 3, and 4 showed significantly lower DC than control group and group 1 (p<0.05). In conclusion, residual primer decreased μTBS and interfered polymerization of adhesive resin. Therefore, the evaporation of residual primer is needed for proper bond strength and Polymerization of two-step self-etch adhesive system.