Pressure drops in air-water two-phase flows in a four by four rod bundle with partial length rods (PLR) are measured by using differential pressure transducers. The sampling frequency is 0.2 kHz and sampling number is 50000. The experimental apparatus consists of an acrylic channel box and 16 stainless rods. Air and water at atmospheric pressure and room temperature are used for the gas and liquid phases, respectively. The ranges of the gas and liquid volume fluxes, J_G and J_L, are 0.4 < J_L < 2.0 m/s and 0.06 < J_G < 8.85 m/s, which cover typical two-phase flow patterns appearing in the fuel bundle. As a result, the following conclusions are obtained: (1) Although the pressure drop decreases with increasing the number of PLRs, the magnitude of the pressure reduction scarcely depends on their locations. (2) The pressure drop is well evaluated by using the void correlation proposed by Ishizuka et al. and the homogeneous model for the frictional pressure drop.