Background Mitogen-activated protein kinase (MAPK) cascades play pivotal roles in mediating biotic and abiotic stress responses. In plants, MAPKs are classified into four major groups (A-D) according to their sequence homology and conserved phosphorylation motifs. Members of group A and B have been extensively characterized, but little information on the group D MAPKs has been reported. Results In this study, we isolated and characterised GhMPK16, the first group D MAPK gene found in cotton. Southern blot analysis suggests GhMPK16 is single copy in the cotton genome, and RNA blot analysis indicates that GhMPK16 transcripts accumulate following pathogen infection and treatment with multiple defense-related signal molecules. The analysis of the promoter region of GhMPK16 revealed a group of putative cis-acting elements related to stress responses. Subcellular localization analysis suggests that GhMPK16 acts in the nucleus. Transgenic Arabidopsis overexpressing GhMPK16 displayed significant resistance to fungi (Colletotrichum nicotianae and Alternaria alternata) and bacteria (Pseudomonas solanacearum) pathogen, and the transcripts of pathogen-related (PR) genes were more rapidly and strongly induced in the transgenic plants. Furthermore, transgenic Arabidopsis showed reduced drought tolerance and rapid H2O2 accumulation. Conclusion These results suggest that GhMPK16 might be involved in multiple signal transduction pathways, including biotic and abiotic stress signaling pathways.