Statement of the Problem: Dental injection is one of the most fearful procedures in dental setting, especially for children. Many researchers have attempted to find a painless method. As computer controlled local anesthesia delivery system devices (CCLADs) allow the speed rate and pressure of injection solution to be controlled, they may cause less pain during injection in comparison to the conventional method.Purpose: The aim of this study was to compare pain perception in dental injection by Smartject with conventional technique.Materials and Method: The present study was a randomized single-blind crossover clinical trial. The participants consisted of 50 healthy volunteer dental students.They received a topical anesthetic agent plus injection in maxillary premolar buccal mucosa via conventional technique on one side (control) and a topical anesthetics agent plus injection in maxillary premolar buccal mucosa by Smartject on the other side (experimental). The first injection method was chosen based on block randomization table. A blind person recorded the subjects’ pain perception of injection based on the visual analogue scale (VAS) in the two groups. Repeated measure test, independent Student t-test and Student paired t- test were used. Statistical significance was defined at p< 0.05.Results: There was statistically significant difference in VAS score between Smartject and the conventional technique. The mean of VAS scores for Smartject and the conventional technique were 14.5±7.4 and 24±12.1, respectively.Conclusion: It is suggested, needle penetration is not the main reason of pain during injection. Inconsistent fluid pressure created by injected anesthetic solution on nerve fibers is more impressive in pain development. Hence, Smartject as a CCLAD can be considered as an appropriate device for dental injection. Keywords ● Anesthesia, Local  ● Pain Perception  ● Injections  ● Visual Analogue Scale