Objective: The aim of the study was to test the effectiveness of a chemo-mechanical system, sodium hypochlorite (Carisolv) in comforting the caries removal process in Atraumatic Restorative Treatment (A.R.T.) technique. Method: A group of 56 children aged 10-12 year olds in Pathumtani who had at least one permanent molar indicated for A.R.T technique was randomized by the size of the carious cavities into two groups, Carisolv Group and Conventional A.R.T Group (without Carisolv). An independent single blinded evaluator using three rated categories (good, fair, poor) assessed the completeness of caries removal. The time period from starting to finishing the caries removal process using hand instruments was counted as time spent. Results: The completeness of caries removal by using Carisolv in combination with hand instruments was significantly better than the conventional A.RT. technique (p < 0.001). Obviously, the time spent in caries removal of Carisolv Group (19.7+/-8.8 min) was longer than the conventional A.R.T Group (17.2+/-7.3 min), but it was not significantly different (p=0.24). Conclusion: It could be concluded that Carisolv increased the effectiveness of caries removal process with hand instruments in A.R.T. technique. The study was partially supported by Thammasat University (Thailand) and Mediterm (Sweden).