Abstract: To elucidate the molecular mechanism of the laying process, the differentially expressed genes in the ovary of the laying Zi geese compared with the prelaying geese were identified, and their functions were classified. Suppression subtractive hybridization (SSH) was employed to isolate the differentially expressed genes, and their functional categorizations were predicted by the tool GOTM in search of the Gene Ontology database. The results showed that the subtractive efficiency of the SSH-cDNA library was approximately 20 folds, and the clones were ranged from 300 bp to 750 bp. Eighty-six positive clones were subjected to sequencing and further analysis. Sequence analysis showed that 11 known (including a mitochondrial gene) and 4 unknown ESTs were highly expressed in the ovaries of laying geese compared with prelaying geese. Eleven known ESTs belong to the functional groups of binding, catalytic activity, enzyme regulator activity, transporter activity and other activity. These results indicated that the SSH-cDNA library of the Zi geese ovary was successfully constructed and the expression levels of 15 differentially expressed ESTs were up-regulated in the laying Zi geese ovary compared with the prelaying Zi geese ovary, these ESTs could play an important role in the process of egg-laying.