Congenital agenesis of the seminal vesicle (CASV) is frequently associated with congenital absence of the vas deferens (CAVD) or ipsilateral congenital vasoureteral communication. We reported two cases of a rare condition that the vas deferens open ectopically into Mullerian duct cyst associated with agenesis of the ipsilateral seminal vesicle. The diagnosis was confirmed by vasography. Transurethral unroofing of the Mullerian duct cyst was performed in both patients with favourable results, however, assisted reproductive technology (ART) was still necessary for them to father children.