Nosocomial infection is one of the causes of increasing morbidity and mortality rates in hospitals. Factors causing the occurrence of nosocomial infections can be endogenous factors and exogenous factors. Reusable instruments used in hospitals are exogenous factors of nosocomial infections, so there should be efforts to prevent nosocomial infections by sterilization methods. The purpose of this research is to know sterility of medical equipments after sterilization at Central Hospital Installation Sterile Supply Department (CSSD) RSUD Yogyakarta based on long storage of medical equipments. The type of research used is analytic observational research with cross sectional approach that emphasizes the relationship between the old variable storage and the number of germs. This research was conducted in Central Sterile Supply Department Installation (CCSD) RSUD Yogyakarta with the selection of research samples conducted according to the availability of tools. Samples used in the form of medical equipment that is tweezers as many as 30 samples taken three times, those are on third day, tenth day and fourteenth day. In Installation CSSD RSUD Yogyakarta using steam sterilization technique pressurized with conventional pressure steam engine. The analysis used is univariate and bivariate analysis, that is correlation test. The results showed that sterility test of medical equipment after sterilization at CSSD Installation RSUD Yogyakarta not yet included in good category. The number of germs in the post-sterilization medical installation at the CSSD RSUD Yogyakarta installation based on the storage period of the 3rd day, 10th and 14th more than the specified maximum limit. Differences in the number of medical device numbers based on the 3rd, 10th and 14th day storage days at the CSSD RSUD Yogyakarta Installation, with an increase in the average number of germs from 24 CFU / cm2, 71 CFU / cm2 and 156 CFU / cm2.