The present invention relates to a use of a human small leucine zipper protein in the adipocyte differentiation procedure. More specifically, sLZIP binds with PPARγ2 to induce the formation of a complex of HDAC3 and PPARγ2, thereby functioning as a corepressor to negatively inhibit the transcriptional activity of PPARγ2 and suppress the differentiation to adipocytes, and thus can be used as a marker for treating diabetes and obesity and developing new medicines therefor.