To investigate the expression patterns of histone acetyltransferase (GCN5) and histone deacetylase 1 (HDAC1) in preimplantation mouse embryos and the effects of in-vitro cultures on their expressions, immunocytochemistry was used to detect the expressions of GCN5 and HDAC1 in mouse embryos at the stages of two-cell, four-cell, eight-cell, morula and blastocyst in both in-vivo and invitro groups. In in-vivo group, the obvious expressions of GCN5 were observed in the cytoplasm of all kinds of mouse embryos but blastocysts. Meanwhile, HDAC1 was highly expressed in the nuclei of four and eight-cell embryos and morula but mainly seen in the cytoplasm of two-cell embryos. In blastocysts, the HDAC1 fluorescence was limited to the nuclei of trophoblast cells. In in-vitro group, there were no obvious GCN5 expressions in all kinds of embryos and the expression of HDAC1 was significantly reduced although its expression pattern was similar to that of in-vivo group. Those results showed that in -vitro culture environments could inhibit GCN5 expression and decrease the expression of HDAC1 in mouse preimplantation embryos, which might affect the correct embryonic gene expression.