Statement of Problem: The most important aspect of child behavior management is pain control. Since dental injection is usually considered as the most stressful procedure in dentistry, good pain control during injection and dental procedures is a major factor affecting children's cooperation.Purpose: The purpose of this study was to compare pain perception and efficacy of anesthesia in inferior alveolar nerve block using 27- and 30-gauge short needles.Materials and Method: In this clinical trial study which was conducted according to a split-mouth design, 27- and 30-gauge needles were used for all patients. Forty patients between 5 and 8 years of age requiring local anesthesia for pulpotomy teatment in both mandibular second primary molar teeth were selected. Immediately after injections, pain ratings were obtained using face and SEM scales. Both nurses and children were blind about the type of used needles. Data were analyzed using Wilcoxon Matched-pairs Signed-ranks Test.Results: The 30-gauge resulted in significantly lower pain than 27-guage needles. The success rate of local anesthesia technique was 95% for both types of needles. There was a significant correlation between the two pain measurement methods for both gauges ( p < 0.01). The mean intensity of pain was higher in girls than boys with both gauges. There was no significant difference between age groups regarding pain intensity.Conclusion: Due to the less pain experience and similar efficacy with the use of 30- copmared to the 27-gauge short needles, it can be concluded that the use of 30-gauge needle is more appropriate for inferior nerve block anesthesia in children.Key words: Pain perception, Anesthesia success rate, 27- and 30-gauge needles, alveolar nerve block.