In primary culture of rat hepatocyte, the effect of additives such as some anti-oxidative agents was studied. Among amino acids, proline and histidine were found to be effective on the maintenance of albumin secretion rate. Proline addition resulted in 3 times higher secretion rate until 5th day. In the medium containing transferrin, superoxide dismutase or catalase, 1.5 to 2 times higher level of the rate was also obtained.