An experimental study has been performed to determine the effect of increase in biodiesel moisture content during storage. In the present investigation biodiesel produced from beef tallow and used cooking oil were used. Samples were prepared in 20 L airtight fuel containers and maintained in standard room conditions (about 24 °C and 50 % relative humidity) and were storedfor 40 d. Moisture content was tested on daily basis, whereas other parameters (density, energy content, flash point, cloud and pour points) were tested on the first day of each week. Moisture content showed an increase of 29 % for beef tallow biodiesel and 23 % for used cooking oil biodiesel, from the threshold of 0.5 mg/g (ASTM D2709) during the entire storage time. Other physicochemical properties showed negligible variations and correlations which are not statistically significant. The results indicated that biodiesel produced from beef tallow and used cooking oil can be stored for 11 d and 6 d, respectively before moisture content exceeds the threshold of 0.5 mg/g. The findings suggest that biodiesel should be blended with petroleum diesel to increase its life span before its moisture content reaches the threshold. This would also delay biodiesel degradation and ensure good quality.