The environmental conditions under row covers are characterized by the attenuation of strong radiation, the alleviation of the increase of the soil temperature and the maintenance of the soil moisture and atmospheric humidity in comparison with the conditions prevailing in open fields. The wind-breaking effect and the effect on the preservation of the soil and air moisture were more conspicuous under direct cover as compared with floating cover. However, the increase of the soil and air temperature was significantly suppressed and the damage caused by pests was less pronounced with the floating cover. Germination and early growth of Pak-choi were promoted by covering. Plant height and leaf area of Pak-choi increased, while the dry matter decreased under the covers, resulting in a more etiolated plant growth. The quality of the products was satisfactory. The optimum environmental conditions for the growth of Pak-choi were as follows: air temperature, 25℃; soil temperature, 25℃; soil moisture, pF 1.25-1.75; wind velocity, 0.4-1.4 m/s and higher relative humidity (80%). Row cover appears to be suitable for use in the tropics as well as in the subtropics.