Microcrystalline cellulose (MCC) is a very popular excipient in pharmaceutical market. Consumption of MCC is increasing day-by-day. Influence of temperature and relative humidity (RH) on microcrystalline cellulose changes physical parameter of MCC such as moisture content, bulk density, Carr’s index and flow. Moisture content variation has effect on tablet hardness and friability of tablet. Two grades of HiCelTM MCC are used in this study, one is HiCelTMXLM90 (it is extra low moisture grade of HiCelTM MCC, other properties are same as HiCelTM90M MCC) and second is HiCelTM90M MCC. In this study, we will investigate the effect of different temperature and relative humidity on packed and unpacked microcrystalline cellulose HiCelTMXLM90 and HiCelTM90M during 30 hrs. Both packed and unpacked grades of HiCelTM were taken and sampling was done at different-different time intervals, to evaluate physical parameters of MCC. Tablets were made from all samples. Tablet parameters like test hardness, weight variation and friability were evaluated.