To investigate vegetative growth characteristics of soybean cultivar ‘Fukuyutaka’, major cultivar in western Japan, and ‘Misato-zairai’, local cultivar in Mie prefecture, we measured the response of plant length and total dry weight of these two cultivars to soil water treatment in summer and autumn. Plant length in wet soil condition (control) were significantly longer than that of drought soil condition (drought) in both summer and autumn. In control, plant length in autumn was shorter than that of summer and this difference between the treatment in autumn was small in both cultivars. Similar tendency was found in stem length, and there was a significant effect of treatment and the difference in the treatment between seasons. Among the components of stem length, significant effects were found in main stem node number (treatment in Fukuyutaka; all effects in Misato-zairai) and internode length (the difference between seasons in Fukuyutaka). Total dry weight of control plants was greater than that of drought in summer. In autumn, however total dry weight of control decreased so that both treatments had similar values in two cultivars. Similar tendency was found in total leaf area. Significant effects on relative leaf area growth rate were found for the difference in the treatment between seasons (Fukuyutaka and Misato-zairai), treatment and for treatment and the season × treatment interaction (Misato-zairai). These results suggested that the difference in the response of plant length and total dry weight to soil water condition was different between seasons, but the significance of the effects on these components differed between the two cultivars.