This research focuses on the changes of return period for nonstationary rainfall data in which exceedance or nonexceedance probability varies depending on time. We examined two definitions of return period under nonstationarity and also performed nonstationary frequency analysis using the nonstationary Gumbel model to investigate variations of return period in Korea. Seogwipo, Inje, Jecheon, Gumi, Mungyeong, and Geochang were selected as subject sites of application. These sites have a trend in rainfall data as well as having more than 30 years data. As the results of application, the return periods considering nonstationarity are different with those considering stationarity. The differences of return periods between nonstationarity and stationarity increase as growing return period increases. In addition, the return period using the expected waiting time method shows lower value than that using the expected number of event method.