One of the most commonly considered adaptive designs is a two-stage seamless adaptive trial design that combines two separate studies into one single study such as a phase I/II or a phase II/III seamless trial design . In many cases, study endpoints considered in a two-stage seamless adaptive design may be similar but different. In this case, it is a concern that how the data collected from both stages should be combined for the final analysis. Besides, it is of interest to know how the sample size calculation should be done for achieving the study objectives originally set for the two stages. In this presentation, the methods with examples for sample size calculation by controlling the overall type I error at the pre-specified level are presented.