Abstract: We used ultrasonic-assisted extractioncombined with single factor experiment to determine the dynamic changes of total phenolic and total flavonoid content from different parts of Juglans mandshurica Maxim,and measurethe inhibitive effect of extract from J.mandshurica on tumors. The optimum extraction conditions were ethanol extract fraction of 60%, extract time of 40 min, solid-liquid ratio of 1:20 and extraction temeperature of 30℃. According to the optimized extraction condition parameters,total flavonoid content, total phenolic content in J.mandshurica were significantly different during growth.Total flavonoid and phenolic contentextracted from leaves and sprig from May to Julyare higher than that from August to October. Total flavonoid and phenolic content in J.mandshurica leaves from July were the highest(12.56±0.33 and 76.98±3.73 mg·g^-1).However,total flavonoid and phenolic content in the bark were decreased with the growth of J.mandshurica. In vitro anti-tumor studies show extracts from J.mandshurica leaves can inhibit the growth of SMMC-7721, MCF-7 and KB cells.Extracts from the leaves of J.mandshurica in July significantly can inhibit the growth of MCF-7 human breast cancer cells, and the IC₅₀ is 0.24 mg·mL^-1.