A shoot elongation model was constructed for prediction of mulberry growth that tried to use the length as a growth index. In the model, the shoot elongation rate was represented as the product of growth activity (GA) and potential rate (PR) which were defined as growth activity of mulberry shoot tips and the potential rate of shoot elongation realized at the maximum GA under a given environmental condition, respectively. GA and PR were functions of temperature, photoperiod and/or shoot length. The model was applied to shoot length data of three cultivars grown in a wide area in Japan, and its parameters were determined. The shoot lengths calculated by the model were similar to the measured values and represented annual fluctuation well. The model also showed good estimation of data which were not used for determining parameters. Therefore, the model is practical and seemed to represent the response of mulberry vegetative growth to temperature and photoperiod well.