Abstract: UV and NTG were used to mutate HET-4. Firstly, HET-4 was exposed in ultraviolet 150 s, obtaining a new strain. The acid-producing ability of the new strain is 57.85°T, higher 3.05 % than that of the original strain.When HET-S was disposed with 0.3 mg/ml NTG for 60 min, a new strain was obtained, and its acid-producing ability is 58.02°T, higher 6.52 % than before. The new strain was disposed with UV plus NTG for two times, obtaining a new strain HET-4-1, whose acid-producing ability is 83.66°T, higher 30.64 % than before.

Key words: Lactobacillus, mutation, screening, packle