Objective:To investigate the effect of melanoma inhibitory activity (MIA) on mesoderm formation during the embryogenesis of Xenopus lavies. Methods:The MIA sequence of Xenopus lavies was verified in EST database,and then cloned into pCS2+ for sequencing. The expression of MIA was detected during embryo development by RT-PCR analysis. The micro-injection of morpholino(MO) was used to knockdown MIA. The expression of marker genes was detected during germ layer formation by whole mount in situ hybridization. Results:The MIA sequence of Xenopus lavies was precisely cloned. The expression of MIA was detected at all the stages during embryogenesis. The knockdown of MIA by MO injection caused the delayed blastopore closure,inhibited the expression of mesodermal marker gene xbra compared to normal embryos. Conclusion:MIA is expressed during embryogenesis of Xenopus lavies,and MIA could play an important role in the mesoderm formation.