In this paper, several experiments were carried out to explore the climatic factors and eco-physiological mechanism related to anthocyanin pigmentation of bentgrass lawn in winter. 1) Shade experiment for analyzing climatic factors on anthocyanin pigmentation was made under the various light and ultraviolet radiation (UVR) conditions with different shading materials. The experiment was made on both turfs of anthocyanin accumulative and non-accumulative strains in winter from Dec. of 1998 to Mar. of 1999. There was high correlation between UVR transmittance and amount of anthocyanin in the leaves, however, there was no significant correlation with light intensity and anthocyanin. This shows that anthocyanin pigmentation is induced by UVR under low air temperature. The same result was obtained in three replicated pot experiment conducted under field condition with four levels of UVR transmittance by shading materials in winter from Dec. of 1999 to Feb. of 2000. 2) Photosyntheses of lawn leaves in different anthocyanin color spot were measured. There was high negative correlation between anthocyanin contents and photosynthetic rate. 3) To make clear the cause of the result above, absorption rate of light and UVR in anthocyanin extracted from the leaf were measured. The anthocyanin extract absorbed light and UVR strongly. These results show that decrease of photosynthetic rate in anthocyanin colour leaves depends on high absorption of solar radiation by anthocyanin in leaves. At the same time, this result suggests that anthocyanin which exists in epidermal tissue will protect mesophyll tissues from the injury of UVR. 4) The temperature of solution extracted from different anthocyanin color leaf rised pararelly to anthocyanin content by sun radiation. This suggests that anthocyanin in turf leaves contributes to increase of leaf temperature in winter. 5) Light absorption spectra in both extracts of chlorophyll and anthocyanin obtained from both pot culture plants grown under field (low temperature) and green house (normal growth temperature) in winter were measured at wide wavelength. All absorption spectra in chlorophyll extract were the same. While, those of anthocyanin extract differed by pigment content. That is, in extract with high anthocyanin, absorption spectrum was high value at wide wavelength and had a maximum peak at 500 nm compaired to low anthocyanin extract. These results coincided with the function of absorbance of light radiation and increase in extract temperature of the anthocyanin accumulative strain. 6) These results indicate that anthocyanin has functions of ① protection from UVR injury, ② cutting photosynthetic radiation and ③ rising leaf temperature. These functions in anthocyanin accumulative strain were higher than those of non-accumulative strain under the same solar radiation in winter. It was suggested from above mentioned results that anthocyanin pigmentation of bentgrass turf in winter is a mechanism for eco-physiological adaptation to maintain the balance of production and consumption of photochemical products under low air temperature.