Abstract: 【Objective】To explore the biological characteristics of myocyte enhancer factor-2(MEF2A and MEF2B)and its expression in organs and tissues at different developmental stages of Guanling cattle,in order to provide theoretical reference for revealing the action mechanism of MEF2A and MEF2B genes in the growth and development of Guanling cattle and exploring local germplasm resources.【Method】The coding regions(CDS)of MEF2A(NM_001083638.2)and MEF2B(NM_001145793.1)were cloned by RT-PCR. Bioinformatics analysis was conducted by using ProtScal,NetPhs3.1,SOPMA,ProtParam,PSORT II Preadict,SWISS-MODEL and other online software. At the same time,real-time fluorescence quantitative PCR was used to detect the expression levels of MEF2A and MEF2B genes in organs and tissues of different developmental stages of Guanling cattle(calves,young and adult cattle).【Result】The CDS sequences of MEF2A and MEF2B genes in Guanling cattle encoded 492 and 368 amino acid residues,respectively. The relative molecular weights of MEF2A and MEF2B proteins were 52 and 39 k D,respectively,and the corresponding theoretical isoelectric points(pI)were 9.07 and 9.35. They were basic-unstable protein. The MEF2A and MEF2B proteins of Guanling cattle were dominated by random curling and α-helix,and were localized in the nucleus(60.9% and 52.2% respectively). The MEF2A gene of Guanling cattle was closely related to the MEF2A gene of Norwegian mice and sheep,and the MEF2B gene of Guanling cattle was closely related to the MEF2B gene of yak and sheep. Real-time fluorescence quantitative PCR results showed that MEF2A and MEF2B genes were expressed in seven tissues including heart,liver,spleen,lung,kidney,tenderloin and fat of Guanling cattle at different developmental stages,and were affected by the growth stage. The relative expression level of MEF2A gene in organ tissues of calves was significantly higher than that in young and adult calves(P<0.01,the same below),and the relative expression level of MEF2A gene in heart of Guanling cattle was significantly higher than that in other tissues with the increase of age. The relative expression level of MEF2B gene in young and adult cattle was significantly higher than that in calves,and the expression level in heart,liver and spleen of Guanling cattle was positively correlated with age.【Conclusion】MEF2A gene is highly expressed in the heart of Guanling cattle at different developmental stages,while MEF2B gene is highly expressed in the lung and spleen of Guanling cattle at different developmental stages,but the expression of MEF2B gene is relatively low in the tenderloin. In conclusion,MEF2A and MEF2B genes play an important role in the growth and development of Guanling cattle.