The purpose of this Investigation was to study byscanning electron microscope the effects of Nd:YAGlaser and Gallium-Aluminium-Arsenic ( Ga-AI-As ) laseron exposed dentinal tubules of human extracted teeth.Fifteen 3 mm. thick slices were cut at thecementoenamel junction frorn 15 extracted firstpremolar teeth. By using a diamond bur to remove thecementum layer the dentinal tubules were exposed andetched with EDTA 0.5 Molar for the smear layer removal.The fifteen slices were randomly assigned to 3 groupsfor 1, 2 and 3 minutes lasing time group. Each slice wassectioned into 4 pieces size 3x3 mm. Three pieces werelased randomly by Nd:YAG laser 50 miliijoules ( mj),100 mj. and Ga-AI-As laser for 1, 2 and 3 minutes andthe unlased piece served as control. The specimens weremounted on a stub sputter coated by gold and examinedby scanning electron microscope. The numbers anddiameter of dentinal tubles were recorded. The results showed that there were no significantdifferences in numbers of dentinal tubules in eachgroup by one way analysis of variance ( P>0.05). Atfluences of 50 mj. and 100 mj. of Nd:YAG laser smallestdiameter of dentinal tubules were noted at 3 minutes(1.8197(+,-) 0.4923 um). and 2 minutes ( 1.7764(+,-) +0.7506 um.) lasing time respectively. When lasing timewas 3 minutes, the smallest diameter of dentinal tubulesof Ga-Al-As laser (1 .6715 + 0.345 um.) was found. Allof test groups show significant differences fromcontrol group( P< 0.05 ). The results indicate theapplication of lasers at specific fluences and time canreduce the diameter of dentinal tubules and may befurther used for root hypersensitivity treatment.