We explored the metabolic mechanism of silkworm (Bombyx mori) to NaF by using the fluoride-tolerant silkworm variety named T6 and the fluoride-sensitive variety named 734 as materials. We fed the silkworm larvae from the first day of fifth instar with mulberry leaves soaked in 50, 100, 200 and 400 mg/kg NaF solutions respectively. Then we examined the activities of CarE and esterase in hemolymph. Results showed that the activity of CarE was 73% to 88% in 734 strain and 72% to 81% in T6 strain compared with control groups, respectively. The CarE activity of two low concentration NaF-treated 734 groups showed extremely significant differences(P<0.01) with control group and two high concentration NaF-treated groups, while the differences among T6's all treatment groups were not significant. The esterase activity of NaF-treated groups was 89% to 97% in 734 strain and 73% to 92% in T6 strain compared with control groups, respectively. The esterase activity among all treatment groups in 734 strain show no significant differences. The esterase activity of the highest concentrations NaF-treated group showed extremely significant differences (P<0.01) compared with control group. These results suggest that the fluoride has certain inhibition to the activity of CarE and esterase in hemolymph of silkworm.