Alveoli are the key functional units of the lungs where gas exchange take place. But the regulation of alveolar morphogenesis is not completely understood. The basic strategies of mammalian lung development can be generally divided into two stages: epithelial branching morphogenesis, and septal formation. P311 was identified previously as a gene that specifically expressed during lung septal formation. In order to further explore the potential effects of P311 during lung development, a yeast two-hybrid screen was performed to identify P311 interacting partners. A recombinant P311 fused with the Gal4 DNA binding domain was used as the bait protein to screen a cDNA library constructed from developing mouse lungs. After confirmed by coimmunoprecipitation (CoIP) and bimolecular fluorescence complementation (BiFC) experiments, SPARC (secreted protein, acidic and rich in cysteine) was identified as a P311 binding protein. In further studies, it was found that SPARC showed similar temporal expression pattern with P311 during lung development. Double immunostaining indicated SPARC and P311 colocalized in alveolar epithelium and myofibroblast in P11 mouse lung sections. Taken together, the data suggested that P311 might have a close connection with SPARC on its influences on lung development.