Abstract: LFY and its homologs are key integrators controlling the vegetative-to-reproductive transition in higher plants. A better understanding of flowering-time genes possesses practical applications for shortening tree juvenility and improving flower bloom period. To examine the effects of amino acid sequence changes of LFY on its function in Arabidopsis, the phenotypic variation and sequence characterization of lfy2 and lfy5 were investigated in this study. The results showed that although lfy2 and lfy5 derived from different ecotypes of Arabidopsis, the phenotypic variations of mutants were similar. The flowering time of lfy mutants was 14 days later than wild-type,the numbers of cauline leaves and lateral shoots were increased, and the floral organs were missing and homeotic. Sequence analysis revealed that the amino acid mutation sites of LFY were P236L in lfy2, and F42L, V209A and P236L in lfy5 with F42L and V209A being at non-conserved sites. Q-PCR analysis showed that the transcript levels of FLC and TFL1 were increased in the inflorescence of lfy, and those of FT and AP2 were decreased, while AP1, AP3 and AG were not expressed. These results suggest that mutation at the site of 236 on LFY-C domain caused the loss of LFY function and was responsible for the mutant phenotype in lfy2 and lfy5.