Abstract: One year old seedlings of Ginkgo biloba L. which grew in a pot under greenhouse conditions with varying soil water levels was nsed to study the effects of water stress on uhrastructure of mesophyll cell. Four soil water levels, i. e., 80%. 60%, 40% and 20% of field capacity, were employed, and the time of treatment was 110days. The results showed that at the soil water level of 80% of field capacity, the karyon was normal, and the karyotheca was clear. Some starch particles anti plastoglobulis were seen in few chlornplast, and much atrament was seen in the cytoplasm, too. A! the soil water level of 60% of field capacity, the mesophyll cell and karyon were normal, and the karyotheca and ehloroplast lamellae were clear basically. There were few plastoglobulis and starch particles in the chloroplast, and the atvament was seen in the eyloplasm, ceil wall and chloroplast ectoblast, too. At the soil water level of 20% of field eapaeily, much of karyotheca and chloroplast lamellae disappeared, and the plastoglobulis became much more and bigger. At the soil water level of 40% of field capacity, the karyotheca, chloroplast ectoblast and chloroplast lamellae disappeared basically, and there were more and more plastoglobulis in the chloroplast.