Soil temperature in spring Chinese cabbage field unmulched and mulched with rice-straw, transparent polyethylene (PE) and black polyethylene was checked at 5, 10 and 15 cm depth under the soil surface. Minimum, mean and maximum soil temperatures at each soil depth were almost always highest in the plot mulched with the transparent PE film and followed by black PE mulch. Those of the plots of rice-straw mulch and the unmulched check were almost equal and lowest. Daily minimum and maximum soil temperature at 10 cm soil depth were shown in the highest frequency at 7:00 and at 16:00, respectively, regardless the mulch materials. The time showing minimum and maximum soil temperature in a sunny day occurred about one hour later as the soil depth was lowered to 15 cm, regardless of mulch materials. [AS]