[Objectives]  To understand the effect of lead on the fecundity of the beet armyworm. [Methods]  the effects of different concentrations of dietary lead (0, 0.3, 4.8, 76.8 mg/kg) on the fecundity of five successive generations of the beet armyworm were measured and compared. [Results]  Increased lead concentration affected the sex ratio of later generations, especially the 3^rd and 4^th generations in which the proportion of female offspring reached 50% at high dietary lead concentrations, significantly higher than in the control. The production gland index, number of eggs and hatching rate were also highly correlated with lead concentration and generation; the more generations and the higher the lead concentration, the smaller the production gland index, the lower the number of eggs produced and the lower the hatching rate. Compared to the control group, the high lead (76.8 mg/kg) treatment group had significantly reduced gonad and oviposition indices. The gonad index was just 60.4% that of the control, whereas the number of eggs laid and the hatching rate were 60.5% and 6.2% those of the corresponding control group. [Conclusion]  The effect of dietary lead on the fecundity of the beet armyworm increased with the lead content of the diet and generation.