The aim of this study was to measure and compare the micro shear bond strengths of the following dentin bonding systems to the dentin surfaces under simulated pulpal pressure: All Bond $2^{circledR},{;}Second^{circledR},{;}AdheSE^{circledR}$, Adper Prompt $L-Pop^{circledR}$. The occlusal surfaces of 180 extracted human molars were prepared so the dentin bonding surfaces could be exposed. The teeth were randomly assigned to 3 equal groups of 60 each and subdivided. The dentin surfaces were treated with the above mentioned bonding system and resin composite cylinders were built up under a simulated pulpal pressure when saline (Group II) or diluted bovine serum (Group III) was used as the pulpal fluid. As a control. the same procedures were performed in the dried dentin surfaces (Group I). After one day of storage in water. the micro shear bond strengths were measured using an EZ tester. Group II and III showed significantly lower shear bond strength than Group I statistically (p < 0.05). $SEbond^{circledR}{;}and{;}AdheSE^{circledR}$ showed no difference among the different dentin condition. In the Adper Prompt $L-Pop^{circledR}$. a simulated pulpal pressure were applied to the specimens using diluted bovine serum. which showed a higher strength than the specimens in which saline was used (p < 0.05).