This study was conducted to investigate the effect of cultural conditions and nutritional components on the cell growth and bacteriocin production of Lactobacillus plantarum KC21. In cultures without pH control, the bacteriocin activity of L. plantarum KC21 was higher at $30^{circ}C$, however, the cell growth rate was higher at $37^{circ}C$. In MRS broth with an initial pH 6.0, the cell growth was lower, but high bacteriocin levels were recorded than at pH 7.0. The bacteriocin activity was maximal in medium containing 1.0 or 1.5% glucose or 1.0% lactose. Yeast extract (0.25 or 0.5%) added to MRS broth increased the bacteriocin activity, moreover, the bacteriocin in the presence of 1.0 or 3.0% NaCl, 0.5% $NH_4PO_4$, or 0.25 or 0.5% $KH_2PO_4$ resulted in the activity of 12,800 BU/mL, but excessively high salts concentration hindered the cell growth and bacteriocin production significantly. Besides 1.0 or 2.0 mM $MgSO_4$ highly increased the bacteriocin activity without affecting the growth of L. plantarum KC21, and ascorbic acid (1.0 or 3.0 ppm) enhanced the bacteriocin activity up to 2 fold.