This study aims to compare the 1,4-dioxane removal functions of four willow (Salix spp.) strains during the two seasons (summer and autumn) and to elucidate the function of phytoremediation (volatilization, metabolism, and accumulation) of 1,4-dioxane-containing water by willow during the two seasons. This investigation tests the removal performance of 1,4-dioxane from solution by the strains; KKD strain which shows extremely fast-growing, HB471 which shows similar characteristics as KKD, FXM strain which shows relatively strong drought tolerance, and SEN which shows relatively strong insect resistance. Pot tests of 1,4-dioxane removal by willow revealed significant differences in removal rates between the summer and autumn seasons. In all four willow strains, the autumn removal rates decreased to 15.7 to 25.4% of the summer removal rates. The strain with the highest removal rate was KKD (37.5% of the exposure) during the summer season, making it the most promising strain. When comparing the percentage contribution of 1,4-dioxane removal by plant function in KKD, removal by transpiration was the largest contributor in both summer and autumn. However, in the autumn season, the contribution of transpiration to 1,4-dioxane removal was smaller, while the contribution of accumulation increased. This occurred because transpiration decreased during the autumn, causing 1,4-dioxane absorbed from the roots to remain in the plant body instead of being transpired. Considering the application of willow in arid lands, the importance of water management was suggested, as a decrease in transpiration was found to affect removal performance.