Thymosin-β4 (thymosin-β4, Tb4) is an important G-actin sequestering factor in cells, which could regulate the activity of G-actin in various microfilaments events. Previously, many researches have reported that Tb4 has broad cellular and physiological functions, but until now, there is lack of systematic research on mammal oocytes and early embryonic development. Tb4 is a small hydrophilic peptide, initially, which separated and purified from bovine thymus component Ⅴ, with a molecular mass of 5 ku, and compose of 43 amino acid residues. Tb4 molecule is highly conservative, which has been founded in a variety of tissues and organs in vertebrates, and also exists in part invertebrates. This peptide has extensive biological functions. Recent studies have shown that it closely relate with many physiological and pathological activities, such as immune regulation, neurological development, wound healing , inflammatory response, angiogenesis, apoptosis, tumor occurrence and migration. Dynamic events of microfilaments in cells always accompany with G-actin activity, while Tb4 could bind G-actin with a ratio of 1∶1 to inhibit G-actin to polymerize into microfilaments. In cells, nearly half of G-actin are bound with various of sequestering factors, which effects on both G-actin activity regulation and its reservation, while Tb4 is the chief executer of G-actin sequestering factor family. The ovaries, oocytes and early embryos of Kunming mouse was used to investigate the expression and distribution of Tb4 in oocytes and eary embryos. During the experiment, the immuno-histochemistry, immuno-fluorescence-histochemistry and RT-PCR technique were utilized as chief study methods. The discipline of Tb4 expression and distribution in oocytes maturation and early embryonic development were studied both in vivo and vitro. The results showed that Tb4 were different in expression and localization during mouse oocytes maturation and early embryonic development. Immuno-histochemistry results illustrated that, accompany with follicle growing, the expression amount of Tb4 peptide in vitro oocytes is gradually increased. There are different distribution characteristics of Tb4 in GV stage oocytes, which featured by chromatin configuration, such as divided the configuration into NSN, pNSN and SN type. In other stages of oocytes maturation and early embryonic development, Tb4 could locate both in nuclear and cytoplasm, and the expression amount always changing regularly, which are closely related with cells growing status and the cell cycle. AIOD value of Tb4 was not significantly different in the process of oocytes maturation in vivo, but the fluorescence intensity rapidly increased form 8-cell embryos to blastula stages in the process of embryonic development. The tendency of Tb4 mRNA transcription are similar to the peptide expression in those stages. Specifically, in early implantation blastula, Tb4 peptide highly expresses in implanted lateral cells of blastula, indicating that Tb4 can regulate the microfilaments depolymerization in embryos implantation, so Tb4 plays an important role in the process of embryos implantation. The research concluded that, Tb4 could regulate microfilaments events (such as polymerization and depolymerization) and proliferation of cells in the developmental processes through the changes of its expression and localization. Overall, Tb4 plays an important role for mouse oocytes maturation, early embryonic development and embryos implantation.