Purpose: We observed the actual half life of the alpha-fetoprotein (AFP) had clinical meaning in that it reflected the long term prognosis more individually at a certain level of preoperative alpha-fetoprotein. Methods: From preoperative and postoperative measurements of alpha-fetoprotein in 96 hepatocellular carcinomas the actua1 half lives were calculated with the formula: AHL T1/2 (days) = -0.3× (T/log(C1/CO)), where T was the time interval between C1 and CO, in which C1 meant the level of AFP at postoperative 7 day, CO the original AFP level. We investigated overall survival and disease free survival rate between delayed AHL group and non-delayed AHL group under various definitions of delay. Results: The average actual half life of all cases was 5.1±13.6 days. One, three and five year overall survival rates of the group with actual half life less than 4 days were 82.1%, 66.7%, 61.1lo respectively, whereas those of the group with actual half life more than 4 days showed 83.0%, 36.5%, 18.2% respectively. The significance of different survival rates was much higher, when only the patients with preoperative alpha-fetoprotein above 100 ng/ml were taken into account (n=53, P=0.0019). The disease free five year survival rates were also significantly different. Conclusion: We can predict the elevated postoperative survival rate in the patients with actual half life of alpha-fetoprotein less than 4 days. And this has also relevant clinical meaning in the prognostication of disease free survival, if the preoperative alpha-fetoprotein of patients has elevated up to over 100 ng/ml. The measurement of actual half life of postoperative hepatocellular carcinoma patients can be clinical useful parameter for the prognosis of long term survival. (J Korean Surg Soc 2001;60:644-648)