Abstract: The aim of the study is to determine the optimum LaCl3 concentration in culture medium of mulberry tissue seedling by testing the influence to the growth and differentiation of mulberry tissue seedling from LaCl3 on different concentration. Based on the work of predecessor about the influence of the rare earth element to the plant physiology biochemistry, different mass concentration LaCl3 are chosen for culture medium to test the differentiation and growth of mulberry tissue seedling . The results show that low mass concentration rare earth element LaCl3 (40 mg/L) can accelerate the growth and differentiation of mulberry tissue seedling. The plant height, the differentiated shoot rate, the root rate, the root length and the weight of mulberry tissue seedling are all better remarkably than the control check and the other mass concentration treatment. Plant height is 63.5% higher than the control check treatment. Rooting rate is 12.5% higher than the control check treatment. Differentiated shoots is 84.2% higher than the control check treatment. At the same time the low mass concentration rare earth element LaCl3 (40 mg/L) can also increase chlorophyll content. The content of chlorophyll a and the content of chlorophyll b are 2.06 times and 1.64 times of the control check treatment respectively. Low mass concentration rare earth LaCl3 (40 mg/L) can also change proportion of chlorophyll, and enhance POD activity. The high mass concentration LaCl3 (60 mg/L, 80 mg/L) reduced or even restrain the growth of mulberry tissue seedling. Therefore, the optimum mass concentration of the rare earth element LaCl3 that can promote differentiation and rooting of mulberry tissue seedling is 40 mg/L