Venous air embolism is a rare complication during transurethral resection of the prostate (TURP). We report a case of air embolism during TURP under general anesthesia in a 56-year-old man. Incorrect assembly of the resectoscope-drain aspiration system caused rapid entrainment of air into the vein of the prostate bed. Rapid recognition of the condition and prompt treatment are required.