Abstract: For the regulatory mechanism of floral organ development in orchid, PhalPI gene(GenBank accession number:KY020416) was cloned from Phalaenopsis petals. By the sequence analysis, the cDNA full-length of this gene was 944 bp encoding 210 amino acid residues. The gene belongs to the GLO/PI group of the B class MADS-box transcription factor, which was highly identified with PhPI10 and PeMADS6 from Phalaenopsis. The PhalPI was expressed in reproductive organs and not in vegetative organs, the expression level was reduced in ovary after pollination. In 5 floral organ mutants, the expression level of the PhalPI gene was higher significantly in sepal and column of lip-like sepal mutants than that of the normal. The expression of this gene was decreased in sepals and petals in petal-like stamens mutant, and it was increased significantly in lip and column in this mutant. In column of Lateral petals pillared mutants, the expression of PhalPI gene was also increased significantly. The changes of expression level of the PhalPI gene in 3 floral organ mutants were associated with morphological mutations of floral organ. However, the expression levels of PhalPI gene were not changed in lip-like Lateral petals and anther-like Lateral petals mutants. Therefore, the PhalPI gene plays a crucial role in regulating Lateral petal and lip development in Phalaenopsis.