A gas-liquid two-phase flow in narrow channel is encountered in mini-scale devices, such as a separator for polymer electrolyte fuel cell. In the present investigation, detailed observation on pressure drop fluctuation characteristics in narrow channel were carried out. The test channel has a square cross section that has 2.0mm on a side. In order to investigate the influence of the return bend, we applied return U-shaped return bend and a return bend with a sharp 180-degree turn. Furthermore, in order to the influence of the wall wettability, water-repellent and attracting treatment were applied to the acrylic channel, respectively. In our previous study, in the straight section except as water-repellent channel, the fluctuation of the pressure drop could be correlated by the Lockhart-Martinelli parameter. On the other hand, in the return bend with a sharp 180-degree turn, it was hard to be correlated by the Lockhart-Martinelli parameter due to the centrifugal force. Furthermore, in the present investigation, even though in the return bend with a sharp 180-degree turn, it was cleared that the fluctuation of the pressure drop could be controlled by the wall wettability.