S terilization of dental instruments after being used for patient treatment is very important because the instrument will be used again on the next patient, if sterilization is performed less well then the contamination can occur in next patients. The purpose of this study to determine the role of cleanliness of instruments such as the mouth mirror and handpiece that has been sterilized, whether it can cause cross­ contamination or not. The method used in this study was experimental laboratory, by swab on the instruments such as mouth mirror and handpiece before and after sterilization. The results of 15 dental practices obtained 73.33% using the autoclave and 26.67 % using the dry oven as sterilization equipment. From the culturing of microorganisms obtained 2 types of bacteria such as Staphylococcus a/bus and Streptococcus alpha, after the sterilization has done no longer bacteria life. The ability two kind of these sterilization equipment on sterilization of the handpieceindicates p = 0.637 which proves that the ability of sterilization is very significantbecause p> 0.05, as well as sterilization of the mouth mirror p = 0.593 showed the significantly because p> 0.05. Conclusion from this study showed the sterilization performed by dental practices in West Jakarta area is good and can be applied to other dental practices.