Purpose: This study compared the bacteria levels in cavities prepared by Er:YAG laser and by conventional means. Materials and Methods: Twenty-one cavities were prepared by Er:YAG laser ablation and 19 by the conventional technique. A sample was taken from the inner aspect of each cavity with a sterile swab and cultured on agar-blood plates. The plates were incubated at 37°C for 24 h, and the number of bacterial colonies was counted. Results: In 90% of the cavities prepared by Er:YAG laser ablation, bacteria were absent, while in the remaining 10%, bacterial cultures were very dilute compared to the results with the conventional technique. Bacteria levels were high in the cavities prepared by conventional means. Conclusion: This study demonstrates greatly reduced bacteria levels in cavity preparation when caries is ablated with the Er:YAG laser.