Purpose: To investigate the efficacy of Nd:YAG laser in cleaning root canals. Materials and Methods: Twenty-four periodontally diseased, single-rooted human teeth scheduled for extraction were used. After taking an initial periapical intraoral radiograph, the teeth were randomly assigned to a test or control group. All teeth were conventionally hand instrumented with K files; 21 were then irradiated with a Nd:YAG laser (test group) and 3 were not (control group). The test group teeth were divided into seven subgroups, each with a different power setting. After hand instrumentation, test and control teeth were extracted. From each root, 12 to 14 sections were prepared perpendicular to the long axis and examined under a light microscope. Results: Microscopic analysis showed neither dentin nor soft tissue debris in the canal of any specimens from the 2.0 to 3.0 W power range groups. Conclusion: This study provides evidence that the Nd:YAG laser at certain power settings is able to clean root canals thoroughly.