The objective of the present study was to maximize production ofrennin units (RU) from calf vells and to study impact of clarification andstorage on the final yield of RU. In this respect, three extracting solutions A, Band C were used. Solution A consisted of 3% boric acid, 7% sodium chloride,0.3% calcium chloride and 0.3% sodium benzoate (pH 5.2-5.3), solution Bconsisted of 2% boric acid, 10% sodium chloride and 0.2% sodium benzoate(pH 6.4-6.5) whereas solution C consisted of 4 % boric acid and 0.2%sodiumbenzoate (pH 4.6).Extraction was carried out twice during ten days of soaking.The attained results revealed that the total RU/g of 206.32 RU/g was obtainedwhen solution A was used before clarification which gave the total RU/g of310.78 after clarification. Milk clotting activity (MCA) was the highest whensolutions A was used (pH 5.2-5.3) whereas the minimum values were at pH6.4-6.5 (solution B). The opposite was recorded with respect to proteolticactivity (PA). On the other hand, the total loss of RU due to clarification wasthe maximum in case of solution B (3.13%), whereas the minimum one(2.90%) was in case of solution A. Storage period had a pronounced effect on the loss of RU being the maximum effect was recorded when solution B wasused. Much higher losses were recorded with all extracting solutions whenrennen extract was stored at room temperatures.