This study was carried out to evaluate the effect of acid etching versus laser etching of dentin surface on the bonding of Composite and Compomer restorative materials to dentin surface by studying microleakage at the dentin-filling interface, compositional analysis of dentin surface, and Scanning Electron Microscopic (SEM) study of the bonding area. 120 freshly extracted premolar teeth were divided according to surface treatment into three groups. Group I (Acid etching group) contained thirty teeth. Twenty teeth were selected to assess microleakage by forming standardized class V cavity on the buccal surface of the selected teeth. Then, teeth were subdivided into two subgroups with 10 teeth in each. Subgroup (i) delivered composite filling while subgroup (ii) delivered compomer filling according to manufacturer instructions. microleakage at the dentin-filling interface of teeth was examined using dye penetration method. dye penetration scores at occlusal and gingival margins were recorded and tabulated. Five dentin surfaces of five teeth from group I were etched by acid then prepared for compositional analysis of dentin surface by Infra-Red (IR) Spectroscopy. Another Five dentin surfaces were etched by acid then prepared for (SEM) assessment. Group II (Laser etching group) contained ninety teeth, twenty teeth were used for assessing microleakage after laser etching taking similar steps to that of acid etching. Thirty dentin surfaces of thirty teeth were etched by laser with different parameters then prepared for compositional analysis of dentin surface by IR Spectroscopy. Thirty dentin surfaces of thirty teeth were etched by laser with different parameters then prepared for SEM assessment. Group III (Untreated group) contained ten teeth that were left untreated. Five dentin surfaces of five teeth were subjected to IR Spectroscopy assessment. Five dentin surfaces of five teeth were prepared for SEM assessment. The results revealed that acid etching of dentin surface resulted in significant less leakage compared to laser etching. IR Spectroscopy revealed changes in dentin surface structure indicating that there was a reaction occurred by the acid and laser etching. SEM assessment showed more openings of dentinal tubules in case of acid etching, while in case of laser etching, there were a surface structural changes with a melting and fusion dentin surface. Acid etching of dentin gives better results on the bonding of Composite and Compomer filling materials than laser etching and thus gives more successful clinical condition. Further investigations are needed by using different types of laser to get more benefit from applications of laser clinically.