Abstract: The effects of sodium selenite and nano selenium on the growth performance of laying chicks and the development of their immune organs were studied in the experiment. One hundred and twenty Luoman laying chicks were chosen and divided into 3 groups randomly. Group Ⅰ was the controlled group,in which the chicks were fed with basal diet. The chicks were fed with basal diets added with 0.4 mg/kg sodium selenite and nano selenium resp. in group Ⅱ and Ⅲ. The experimental chicks were weighted on the morning when they were 26 and 36 days old. Five chicks of each group were killed,their immunity organs were fetched out for calculating immunity organ index and observation of section. The results showed that the growth performance of 36 days old experimental chicks had significant difference between group Ⅱ and Ⅰ （P〈0.05）and had extremely significant difference between group Ⅲ and Ⅰ （P〈0.01）; the immunity organ index had no significant difference between group Ⅱ ,Ⅲ and Ⅰ （P 〉0.05）; the periarterial lymphatic sheaths and splenic corpuscles of group Ⅱ and Ⅲ became bigger; the bursal cortex of group Ⅱ and Ⅲ became thicker; the thymic cortex of group Ⅱ and Ⅲ became thicker and their thymic corpuscles became bigger. The comparison on group Ⅱ and Ⅲ ,the splenic corpuscles of group Ⅲ changed more obviously. The addition of nano selenium in the feed of laying chicks could promote their growth and strengthen the function of their immunity organs.