In phase II clinical trials, the primary objective is to assess the efficacy of a drug, such that decisions to proceed with further studies and development of the drug are warranted. To detect a measurable effect in an investigation drug, 2-stage design is often used, whereby an interim analysis of the data may result in the decision to terminate the trial early, or proceed with the second stage of the study. Single stage design runs the risk of exposing too many sick patients in need of efficacious drugs to potentially inactive and dangerous drugs; designs of more than 2 stages are often difficult to manage. We applied Simon 2-stage design for a phase II oncology trial. 2-stage sample sizes using Simon optimal design and minimax design are calculated and compared with single stage design. We confirmed that there are ethical and statistical advantages using Simon 2-stage optimal design. Especially for the stage 1 futility test, the Simon optimal design requires fewer patients. A few newer alternative methods that implement adaptive aspects to the 2-stage design such as admissible adaptive 2-stage design and Lin and Shih’s 2-stage design are also discussed.