An infrared thermal imagery was measured concurrently with physiological status in stressed and non-stressed maize and wheat canopies. Each thermal image, composed of 512 (H)×240 (V) pixels with a sensitivity of 0.05℃, was obtained with an infrared thermography system from a distance of 5 to 20 m. The stress-induced physiological depression in photosynthesis was accompanied by an increase in the canopy-surface temperature, which was visualized clearly on the pseudo-color thermal images, while no visible changes were observed directly from the distance. The maximum difference in mean surface temperatures of the stressed and non-stressed parts of the canopy was no less than 4.2℃ in maize and 3.1℃ in wheat. The infrared imagery was effective for detecting physiological depression or for comparing various canopies in their physiological status on a remote and real-time bases.