Biogenic volatile organic compounds (BVOCs) emitted by plants play an important role in the atmospheric chemistry of the troposphere. We conducted f ield measurements of monoterpene emissions from leaves of <I>Chamaecyparis obtusa</I>, which is one of the major tree species in Japan. Diurnal and seasonal variations of monoterpene emissions from <I>C. obtusa</I> were measured at the Kiryu Experimental Watershed (KEW) at 34°58′ N, 135°59′ E in Shiga Prefecture, central Japan. In August and October 2006 and in January and April 2007, the monoterpene emission rate (<I>E</I>), together with the leaf temperature, was measured using branch enclosure methods for a branch of two trees. The obtained data sets revealed that <I>E</I> highly correlated with leaf temperature throughout the seasons. The basal emission rate (<I>E<SUB>S</SUB></I>) under the standard conditions of 30°C, calculated using a widely used emission algorithm, ranged from 0.088 and 4.126 μg g<SUP>-1</SUP> h<SUP>-1</SUP>. The estimated <I>E</I> values were consistent with the measured <I>E</I> values within a root-mean-square (RMS) error of 0.005-0.525 μg g<SUP>-1</SUP> h<SUP>-1</SUP>, suggesting that the emission model can be used to determine the monoterpene emission responses of <I>C. obtusa</I> to temperature. However, the <I>E<SUB>S</SUB></I> values were significantly different between the trees and also different between seasons, indicating that a representative <I>E<SUB>S</SUB></I> value must be obtained from more data sets using more branches and trees.