Abstract: Mitogen-activated protein kinase(MAPK) is a key component in signal substance in plant's defensive reaction and an important signal molecule in response to abiotic and biotic stresses. To reveal the function of its homolog genes in tobacco, a homolog sequence of MAPK was cloned from Nicotiana tabacum and named as NtMAPK. Amino acid sequence alignment analysis showed that NtMAPK gene belonged to MAPK family of cultivated tobacco.Phylogenetic analysis indicated that NtMAPK featured close phylogenetic relationship with rice OsMPK2/OsMPK62, it suggested that it might function similarly to OsMPK62 and related to plant's resistance to pathogens. Under the induction of plant defensive reaction-related signals, semi-quantitative PCR analysis revealed that the expression of NtMAPK was up-regulated by ABA, Me JA and SA.