Effects of feeding different available nitrogen sources from 80 h in erythromycin biosynthesis phase on the erythromycin A (Er-A) production were investigated in 50 l fermenter. Feeding corn steep liquor and yeast extract, the Er-A production was enhanced, while the biotransformation from erythromycin C (Er-C) to Er-A had no increase. When ammonium sulphate was fed at high feeding rate, the maximal Er-A production and ratio of Er-A to Er-C were 7953 U/ml and 98.18:1 at 184 h, respectively, which were higher than that of the control (6742 U/ml and 5.47:1). The feeding ammonium sulphate process was successfully scaled up from 50 l to 25 m(3) fermenter. The maximal Er-A production reached 7938 U/ml at 203 h, which was enhanced by 22.1% compared with the control (6501 U/ml at 192 h). The ratio of Er-A to Er-C was 24.05:1, which was higher than that of the control (4.77:1).