Flow pattern and fluctuation of void fraction of two-phase flow through a vertical channel with contraction were examined experimentally. The two-phase fluid consisted of water and nitrogen gas. The pipe diameters were 0.1[m] and 0.05[m]. which were before and after the contraction, respectively. Superficial gas and liquid velocity were changed form 0.42 to 2.55[m/s] and from 2.26 to 4.53[m/s]. Time series data of void fraction were measured using a single-needle void probe and flow pattern at downstream from the contraction was visualized using a high speed video camera. Intermittent flow was observed at downstream of the contraction. The pulsation can be seen to be caused by wave of bubbles thick and thin. Frequency of fluctuation of the void fraction was almost constant when flow pattern before the contraction was bubble flow. In the case where flow pattern before the contraction was churn flow, the frequency increased with superficial liquid velocity. The frequency was also confirmed with the result of image processing using the movies captured by the high speed video camera.