OBJECTIVE To detect the expression of MAP3K5 and miR-BART22 encoded by Epstein-Barr virus and explore their relationship in nasopharyngeal carcinomas (NPCs). METHODS Fifty-three archived specimens of NPCs and 30 nasopharyngitis specimens were collected for detecting the expression of EBERs and miR-BART22 by in situ hybridization, and the expression of MAP3K5 was detected using immunohistochemistry. Ten fresh NPC and 10 fresh nasopharyngitis specimens were also obtained for determining the protein expression of MAP3K5 by Western blotting. RESULTS EBERs were positive in all the 53 NPC specimens, and miR-BART22 was positive in 49 specimens; all the 30 nasopharyngitis specimens were negative for EBER or miR-BART22. In the 53 NPC tissues, 50 were negative for MAP3K5 expression in the cancer areas but positive in the adjacent mucosal areas, with the other 3 specimens showing a weak positivity (+). In the 30 nasopharyngitis specimens, 25 showed strong MAP3K5 positivity, 3 showed weak positivity and 2 were negative for MAP3K5 (P<0.001). Western blotting showed that the expression of MAP3K5 protein was significantly higher in nasopharyngitis than in NPC tissues (P=0.029). The expression of MAP3K5 and miR-BART22 was inversely correlated (P<0.001). CONCLUSION Compared with the adjacent mucosal tissues, NPC tissues have a lower expression of MAP3K5 but a higher expression of miR-BART22. The expression of MAP3K5 and miR-BART22 is inversely correlated, suggesting the possibility of MAP3K5 to serve as target gene of EBV miR-BART22. miR-BART22 may inhibit the expression of MAP3K5, thus reducing the protein phosphorylation of MAPK pathway downstream genes, inhibiting NPC cell apoptosis, preventing their differentiation and promoting their escape from immune surveillance.