The sterility of injection pharmaceutical preparation is the most crucial requirement to achieve, as it is injected directly to human body, either intravenously, intramuscularly, or other injection routes and once drug is injected, it moves to other parts of the body through blood flow follows the rules of drug distribution and will have direct contact to all tissues and organ [1]. Theoretically, in order to prevent contamination of microbial by inhibiting the proliferation process, especially in multiple dose of injection drugs, in the final formulation of the drug may need special addition of suitable preservative agent in the preparation [2]. The first step to perform this experimental study was by preparing the sterile pharmaceutical preparation, Diphenhydramine Hydrochloride injection at Sterile Pharmaceutical Preparation Laboratory, of Universitas Muhammadiyah Malang, Indonesia. Once the injection drug was ready, the second step conducted sterility test. The most common method used for sterility test in injection drugs is named direct inoculation. It was conducted by preparing sample from diluted solution of the injection drug, and the concentration was divided into five groups of sample 1:1, 1:2, 1:3, 1:4, 1:5, and undiluted sample (with three times replications) has determined certain level of inactivation of benzyl alcohol as its preservative agent, that was undiluted sample in Thioglycolate medium and 1:1 in Casamino medium. The indicator of bacterial growth in the study was Bacillus subtilis for Thioglycolate medium on range of temperature 30°-35 °C, and Candida albicans as an indicator of fungal growth in Casamino medium on range of temperature 20°-25 °C, both of Thioglycolate and Casamino medium were observed for 14 days. Inactivation of preservative agent and sterility test were performed under LAFC condition and it required some controls of LAFC environment to ensure that experiment was conducted under optimum condition and to avoid false positive result. According to those results of our study, the sterility test has indicated that our Diphenhydramine Hydrochloride injection was sterile after over a period of 14 days of observation.