Abstract: The experimental study on local resistance of single-phase and two-phase flows through a spacer grid in a vertical channel with 3×3 rod bundle was carried out under the normal temperature and pressure. For the case of single-phase flow, the liquid Reynolds number covered the range of 290-18007. For the case of two-phase flow, the ranges of gas and liquid superficial velocities were 0.013-3.763 m/s and 0.076-1.792 m/s, respectively. A correlation for predicting local resistance of single-phase flow was given based on experimental results. Eight classical two-phase viscosity formulae for homogeneous model were evaluated against the experimental data of two-phase flow. The results show that Dukler model predicts the experimental data well in the range of Re_l<9000 while McAdams correlation is the best one for Re_l≥9 000. For all experimental data, Dukler model provides the best prediction with the mean relative error of 29.03%. A new correlation is fitted for the range of Re_l<9 000 by considering mass quality, two-phase Reynolds number and liquid and gas densities, resulting in a good agreement with the experimental data.