The dynamics of evapotranspiration (ET) were analyzed and the applicability of the Penman-Montieth equation (P-M) was evaluated for modeling ET during the 15-day production period of sweetpotato (Ipomoea batatas (L.) Lam., cv. Beniazuma) transplants vegetatively propagated in the closed transplant production system (CTPS) at Chiba University. During days 1 - 4 of the 15-day production period, the P-M significantly underestimated ET. During this period, the cuttings were observed to be wilting, mean stomatal resistance to water vapor transfer (rs) was very high, and evaporation rate (E) was the dominant component of ET. Prediction of ET improved significantly on days 5 - 15, with an acceptable accuracy being achieved during days 7 - 15. Time and PPF based functions for predicting rs yielded similar results when used in the P-M. Combining a model to predict E with the P-M equation should allow accurate simulation of ET for the entire production period.