Abstract: It is very important to visually study bubble growth and departure for better understanding of boiling heat transfer in a narrow channel. Bubble growth and departure in a narrow rectangular under atmosphere pressure were visually observed by the wide and narrow side of narrow rectangular channel using high speed digital camera. There is a small interface between the bubble base and heated surface when the bubble is growing in the nucleate site, and the growing bubble shape is almost spherical. The bubble growth laws in different sites are almost uniform under the condition of the same thermal parameters, but bubble departure diameters are obvious distinct because of different sizes of nucleate sites. The bubble growth rate in a narrow rectangular channel is small, and the bubble departure time is long, the bubble growth diameter can be predicted using the amendatory Zuber expression. The effect of thermal parameters on bubble departure diameters of the mean was statistically analyzed in the camera view. Bubble departure diameters of the mean decrease with increasing heat flux, bubble departure diameters of the mean decrease with increasing inlet subcooling, and bubble departure diameters of the mean decrease with increasing bulk velocity.