Mucor L_(42), isolated as the milk clotting enzyme producing fungi in this laboratory, has been extensively tested for optimum medium compositions and optimum growth conditions for the enzyme production and the results obtained could be summarized as follows, 1. The best enzyme production media known contained 83% of wheat bran, 5.4% of potato starch, 3 % of dextrose, 6.0% of skimmilk powder and 0.5% of ammonium sulfate in the same amount of water as total solid. 2. The optimum mineral contents in the media w as known to be 0.025% of MgSO₄·7H₂O, 0.025% of CaCl₂, 0.05% of MnCl₂, 0.025% of FeSO₄·7H₂O and 0.05 of ZnSO₄·7H₂O. 3. The organism produced the most amount of enzyme at 30℃ in 24 hours in the above medium of pH 6.8