p50 is a member of the NF-kappaB family known to be involved in endometriosis. To gain insight into the roles of p50 in the development of endometriosis, we cross-transplanted endometrial fragments from p50 knockout mice to wild-type mice and vice versa, and also autotransplanted the fragments within the knockout and wild-type mice, inducing endometriosis. We then evaluated the size of the endometrial implants, and immunoreactivity to phosphorylated p65 (p-p65), PKCepsilon and TRPV1 in ectopic and eutopic endometrium as well as in vagina. We found that p50 deletion significantly reduces the size of endometrial implants. The immunoreactivity to p-p65 and PKCepsilon, but not TRPV1, was reduced in endometrial implants in p50 knockout mice. Deletion of p50 significantly reduced p-p65 and PKCepsilon, but not TRPV1, expression in eutopic endometrium and vagina. It also disrupts NF-kappaB activation and PKCepsilon expression in eutopic and vagina, suggesting the role of NF-kappaB in regulating PKCepsilon, which plays an important role in nociception. These data show that p50 is involved in the development of endometriosis and may be a promising therapeutic target.