The OECD acute toxicity guideline has been revised recently to protect animal welfare. The GLP authority of the Ministry of Environment, the National Institute for Environmental Research, recommended GLP laboratories in Korea to ufo the revised acute toxicity guideline. This study was carried out to optimize newly adopted OECD test guideline 420 (TG 420). Bisphenol A was selected for test chemical. Following TG420, Bisphenol A was classified as class 5/unclassified group. The revised TG 420 was very effective test in minimizing animal number and classifying chemicals. The method, however had short-coming in evaluation of test results statistically because the test had no control group, and the test should be stopped when animals were dead at the lowest dose or alive at the highest dose. TG 420 required at Least 20 animals to complete the test, but it could result in producing unused animals that need to sacrifice.