Abstract: The study was conducted to evaluate the effects of four dietary digestible lysine levels on the growth performance and serum indices of replacement gilts from 40 to 70kilograms based on corn-soybean meal with isoenergy and the same ideal amino acid pattern.A total of one hundred and twenty two-line crossbred gilts(Landrace×Large White),with 40 kg of average body weigh and similar body conditions were allocated to four groups with three replicates per group and ten per replicate.The gilts were fed with four diets with different digestible lysine(DLys)levels of 0.68%(trial group 1),0.73%(trial group 2),0.78%(trial group 3)and 0.83%(trial group4).The results showed that average daily gain(ADG)(787.43g)were highest and F/G(2.55)were lowest in trial group 3(P<0.05),the concentration of BUN was significantly lower than that in other trial groups(P<0.05),and the concentration of IGF-Ⅰ was no significant difference among the trial groups(P >0.05).In conclusion,the optimum level of DLys in replacement gilt weighting 40 to 70kg based on this experiment were0.78%,or 0.57g·MJ-1 as expressed with digestive energy(DE).