The purpose of this study is to clarify the function of mitogen-activated protein kinase ( MAPK) activity in the reinitiation of the first meiosis in Zebra Fish (Danio rerio) oocytes. The oocyte maturation of D. rerio was induced in vitro by 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DHP). Another group of oocytes were treated by 17α,20β-DHP with U0126,the inhibitor of MAPK phosphorylation. MAPK phosphorylation in oocytes obtained at different culture time points was analyzed with Western Blot, and germinal vesicle breakdown (GVBD) of oocytes was observed. The results showed that MAPK activity in oocytes in response to the 17α,20β-DHP induction ( without U01266 ) was significantly increased at 2 h of culture and was maintained at a high level until 6 h,and GVBD also almost completed at 6 h. In contrast,U0126 completely blocked MAPK phosphorylation in oocytes exposed to 17α,20β-DHP. GVBD rate of oocytes cultured with both of 17α,20β-DHP and U0126 was lower than that of oocytes cultured with only 17α,20β-DHP. The results suggest that MAPK participates in the resumption of the first meiosis in D. rerio oocytes.