The use of conventional dose of bupivacaine for transurethral surgery is associated with a high incidence of hypotension, prolonged motor recovery and discharge time. It may be possible to minimize these undesirable outcomes by using either smaller dose of bupivacaine or small dose of bupivacaine combined with fentanyl. One hundred and forty two patients aged more than 65 years old undergoing transurethral resection of prostate gland (TUR-P) were randomly allocated into two groups receiving either spinal anesthesia with hyperbaric bupivacaine 5 mg plus fentanyl 20 mcg (group 1) or hyperbaric bupivacaine 8 mg (group 1) or hyperbaric bupivacaine 8 mg (group 2). We evaluated the efficacy of anesthesia and their effects on the incidence of hypotension, sensory level, motor blockade and other side effects. The maximal level of the sensory block in both groups was T9. Motor blockade was significantly more intense in group 2 at all times (P<0.05). The incidence of hypotension within 60 minutes was significantly lower in group 1 compared with group 2 (34.25% vs. 59.42%, p = 0.003). There was no other serious side effects. We concluded that the low dose of hyperbaric bupivacaine 5 mg in combination with fentanyl 20 mcg intrathecally could provide effective anesthesia, less intense motor blockade and lower incidence of hypotension compared with bupivacaine 8 mg in TUR-P.