Biodiesel fuel is subject to degradation as a result of its prolonged storage period. The degradation of biodiesel fuel can have a negative impact on its qualities as well as the performance of the engine. These four stages of degradation are hydrolysis, oxidation, thermal decomposition, and bacterial contamination. A consequence of the hygroscopic qualities of biodiesel is the possibility of hydrolysis processes, which might result in the creation of free fatty acids, which can lead to engine corrosion. The presence of water encourages bacterial development in biodiesel, which might result in the formation of deposits. This study aims to investigate the application of silica gel desiccant in fuel tanks with varying biodiesel concentrations. The total acid number is used as the degradation rate parameter, while the number of bacterial colonies is used as the bacterial growth rate parameter. The research was carried out through experiments using tank models over a period of six weeks, with six tank conditioning. With the experiment results, reducing humidity in the fuel tank by applying desiccant can lead to the reduction of biodiesel degradation rate and micro-bacteria growth.