The effect of liquid viscosity on pressure drop and turbulent transition was experimentally investigated for solid-liquid downward flow. Plotting of friction factor against Reynolds number, both of which were defined by using liquid superficial velocity, was examined as a method to evaluate the effect of liquid viscosity on pressure drop. The friction factor correlated well with the Reynolds number. Based on the friction factor versus Reynolds number plots, empirical correlation equations were proposed for friction factor and laminar-turbulent transition Reynolds number, respectively.