The polygalacturonase (PG) gene in Medicago truncatula was analyzed with bioinformatics.Results showed that the length of the gene was 4 150 bp with 1 278 bp coding region encoding 425 amino acids.The protein encoded contains two conserved domains,PL6 superfamily and Glyco_hydro_28,which are related to degradation of cell wall pectin. The homology between PG in Medicago truncatula and PG insome other leguminous plants including chickpeas and red bean was close.Results of gene expression profile and RTPCR detection showed that MtPG expression was significantly enhanced in the root nodules but very low in non-symbiotic tissues including roots and leaves.Three Tnt1 transposons insertion mutants (NF0999,NF5561 and NF4746) were screened by PCR and one homozygous mutant NF4746 was obtained.It is indicated that the MtPG gene may play an important role in the early infection of symbiotic nitrogen fixation in legumes.