Abstract: Bioinformatics methods were used to perform the genome-wide identification of Dendrobium JmjC gene. The expression patterns of DoJMJ in different tissues and their responses to various photoperiods were detected by qRT-PCR. Seventeen JmjC gene family members were identified in the Dendrobium officinale genomic database，and they were divided into five subfamilies（JARID1，JHDM3，JHDM2，JMJD6 and JmjC-only）based on the conserved domains. The number of conservative domains in each subfamily varies；the gene structures analysis showed that the numbers of exons and introns in different subfamilies were different. There were similar exon/intron structures within the same subfamilies. Promoter cis-acting elements analysis revealed that DoJMJ family members contained hormone response elements such as Auxin，ABA，GA，MeJA，SA elements，and environmental signaling response elements including light，drought，low temperature，defense and stress elements，qRT-PCR results showed that the expression of ten members were higher in stem and leaf，a few members showed higher expression levels in root，and all members had lower expression in the fruit of the Dendrobium nobile，which speculated that DoJMJ might play a major role in the developmental processes of stem and leaf. In addition，the family members also exhibited different expression patterns in various photoperiod conditions. Eleven members were highly expressed a 12 h/12 h（light/dark）cycle，and a few members showed higher expression levels in 4 h/20 h，8 h/16 h and 24 h/0 h（L/D）light cycles.

Key words: Dendrobium officinale, Dendrobium nobile, DoJMJ, genome-wide identification, photoperiod