We report a case of neobladder-rectal fistula that developed as an early postoperative complication of radical cystectomy and orthotopic neobladder construction procedures. A 75-year-old man underwent a radical cystectomy and orthotopic neobladder construction using Studer's method for locally invasive bladder cancer (cT2N0M0). The patient had severe watery diarrhea on postoperative day 20, and was diagnosed with a neobladder-rectal fistula based on cystography findings. We inserted a Foley catheter into the neobladder, and performed conservative treatment. Four months after development of the fistula, cystography revealed that it had spontaneously closed. A neobladder-rectal fistula is an extremely rare complication, with no other known reports. Herein, we present this case of neobladder-rectal fistula and discuss its formation, diagnosis and treatment, along with reference to previous reports of neobladder-vaginal fistulas.