Photosynthetic inhibition to temperature were conducted with ginseng(4 year old) and tobacco(var. Bulgaria). The plants were kept under various temperature conditions from 1$0^{circ}C$ to 4$0^{circ}C$ and 440$mu$E/$m^2$/sec for 3 and 6hrs, and net $CO_2$ uptake were measured after 2hrs at $25^{circ}C$. Photosynthetic optimal leaf temperature of ginseng was 21$^{circ}C$ and tobacco was $25^{circ}C$. Stomatal resistance and mesophyll resistance increased at high temperature. Especially, stomatal resistance seemed to have a significant role in determining the temperature responses of photosynthesis. In tobacco photosynthetic capacity was not changed by temperature treatment for 3hrs. However, 6hrs exposure reduced 8% of net photosynthesis at 4$0^{circ}C$ and 12% at 1$0^{circ}C$. Ginseng plants exposed for 6hrs at 4$0^{circ}C$ lost photosynthetic capacity by 83%. Temperature responses of ginseng were very sensitive at above-optimum temperature resulting greater thermal inhibition other than photoinhibition.