The objectives of this study are to propose a remotely measurable plant transpiration transfer coefficient (h_at) and to verify its characteristics under various environmental conditions. The h_at is defined as (T_c - T_a) / (T_p - T_a), where T_c, T_p, and T_a are the temperatures of the canopy, a non-transpiring canopy, and air, respectively. Theoretically, h_at ≦ 1, and determines transpiration from its minimum value (zero) to its maximum value (potential transpiration rate). Five experiments were conducted between 1994 and 1999 to verify the characteristics of h_at, using 3 plant species (sorghum, tomato and melon). Theoretical validation showed that the proposed model agreed well with conventional models. Experimental results showed that the h_at value was approximately equal to the value of the ratio of sensible heat fluxes (H/H_p), and the slope of the regression line between them was close to 1, the intercept was close to 0, and the regression coefficient was r² = 0.70. In addition, h_at was not only an indicator of the water status in the plant root zone, but also an indicator of atmospheric variables. Under waterstressed conditions, h_at was affected mainly by the water status in the plant root zone. Therefore, h_at can be used as an indicator of plant water stress. The main advantages are that h_at can be easily measured and applied under various conditions. Due to its simplicity, h_at is a suitable coefficient for analyzing the process of transpiration and for determining the transpiration rate.