Aim: To evaluate the effects of pulsed KTP (potassium-titanyl-phosphate) laser on decrease of dentinal microleakage of compomer restorations in primary teeth. Method: Twenty four primary molars were selected for the study. After Class V cavity preparations in buccal and lingual surfaces, teeth were divided into three groups: Group I: Control, Group 2: 1 W KTP laser, Group 3: 1.5 W KTP laser. Then cavities were restored with compomer and teeth were thermocycled to 500 cycles, isolated and immersed in 0.5% basic fuchsin for 24 hours. Teeth were rinsed, dried, and sectioned, and microleakage was assessed by dye penetration at the occlusal and gingival surface of the teeth with stereomicroscope (40X). The data were analyzed with Kruskal-Wallis, Mann-Whitney U and Wilcoxon tests. Results: When the scores of microleakage at the gingival margins of the groups were compared, the differences among the groups were found to be statistically significant (p<0.05). At the occlusal margins of the groups, there were no statistical differences (p>0.05). Comparing the gingival and the occlusal margins in the each group, statistically significant differences existed in the Groups 1 and 3 (p<0.05).Conclusions: KTP laser is able to seal dentinal tubules and consequently reduce microleakage towards pulp in primary teeth.