In this study, we fit a parametric model to the duration of hypopnea. Hypopnea is a partial apnea. A total of two hundred and seven events of duration of hypopnea is considered in this study. The parametric model that has been used is gamma, Weibull, log-normal and log-logistic distribution. The most appropriate distribution to fit the duration of hypopnea is analyzed according to sleep stages. The results indicated that Weibull distribution is the best model for light, deep and Rapid Eye Movement (REM) sleep stages.