The critical heat flux of the counter current flow in narrow-annular flow passages (δ = 0.5 ~ 10.0 mm) was examined for the bottom closed and the open system by using R-113 vapor and liquid at 0.1 MPa. When the clearance δ =2.0 mm in the bottom open system, the falling liquid flow rate was restricted by the upward vapor flow, which was expressed well with theWallis type flooding correlation. The heat flux q_EXC at the initiation of the temperature excursion (EXC) was well predicted for both the bottom closed and the open system by considering that EXC occurs when the falling flow rate becomes equal to the evaporation rate under the liquid penetration limiting. In the case of δ = 5.0 mm, the liquid penetration was also restricted, however it occurred at the much lower velocity than theWallis flooding velocity. It was rather predicted with the flooding by the level swell of the two-phase mixture with the falling film. After the heat transfer surface was covered with the two-phase mixture, the EXC was initiated. In the case of δ = 10.0 mm, the EXC started like the pool boiling without any penetration limiting. q_EXC correlation for δ = 2.0 ~ 10.0 mm was derived by considering that the EXC occurs when the mixture void fraction exceeds a critical value.