The present invention relates to a use of a human small leucine zipper protein in the osteogenesis procedure. More specifically, sLZIP increases the transcriptional activity of Runx2 and inhibits the transcriptional activity of PPARγ2, thereby increasing the osteoblast differentiation, so that sLZIP performs an important role in the osteogenesis procedure, and thus can be used as a marker for treating bone disease and developing new medicines.