Chip calorimeters are promising tools for quantitative analysis of cellular metabolic rate. The measurement of cellular metabolic heat can be an excellent indicator of its physiological state and the changes in response to external stimuli such as drugs. We have developed a highly sensitive microfluidic chip calorimeter capable of maintaining cellular activity and controlling the fluid flows of biochemical stimuli around the cells. Using the chip calorimeter, we demonstrated the measurements of cellular metabolic rate by monitoring the changes in power output of a few hundred cells responding to biochemical stimuli.