The purpose of this study is to determine the effect of dietary conjugated linoleic acid(CLA)supplementation of pregnant and lactating sows on muscle growth and myofiber type oftheir piglets.There are thirty healthy,pregnant Rongchang sows withsimilar body condition and closed expected day of parturition for the experiment in vivo.Three experiment groups carry out with/without CLA(1%,2%and 0).The experiment began on 85th day of gestation and ended at 28th day after piglet birth.The results show that 1,piglets from CLA-fed sows had heavier longissimus dorsi and higher percentages of slow myofibers than control piglets(P <0.05).2,moreover,real-time PCR showed that CLA supplementation induce increasingexpression of MyHC 1,MyOG,and MyOD genes while decreasingexpression of My-HC 2a,MyHC 2x,and MSTN genes in piglets.We also check the expression of genes which appear in 2in vitro experiment.c9,t11-CLA acted to induce the differentiation of cultured pig skeletal muscle cells and up-regulatesthe expression levels of MyHC 1 and MyOG,butt10,c12-CLA strongly inhibited cellulardifferentiation and down-regulates expression of MyOG.These findings suggest that dietary CLAduring early life mayaffect muscle development and myofiber type in pigs.