An experiment was conducted to investigate heat transfer characteristics of tap water in micro-channels. The tested channels were rectangular channels with 12mm breadth. They were a straight channel and two curved channels having a curvature radius of 64mm and 32mm, and the channel height was changed from 1.0mmt to 3.0mm. The experimental results can be summarized as follows. 1) Heat transfer coefficient in a subcooled region increases rapidly with decreasing the degree of subcooling. 2) Heat transfer coefficient in a saturated region first decreases and then turns to increase. 3) Heat transfer coefficient in a saturated region increases with decreasing heat flux and increasing mass flux for all experimental conditions. 4) Heat transfer coefficient in a curved channel is smaller than that in a straight channel having the same channel height for narrower channels, but this tendency is reversed for higher channels. 5) Dryout occurs with smaller vapor quality with smaller channel height smaller curvature radius, smaller mass flux and larger heat flux.