In our previous studies, we carried out air-water counter-current flow experiments under flooding conditions in vertical pipes having a diameter of D = 40 mm with combinations of sharp-edged or rounded top and bottom ends, and we measured counter-current flow limitation (CCFL), pressure gradient dP/dz, and void fraction α_G. We obtained the wall and interfacial friction factors f_w and f_i, and proposed correlations for f_w and f_i. In the present study, we carried out similar experiments in vertical pipes of D = 60 mm with rounded top and sharp-edged or rounded bottom ends (R/S or R/R) to evaluate effects of diameters on flow characteristics. For the smooth film (SF) due to flooding at the top end in the region of low superficial gas velocity J_G, the |dP/dz| value was very small and the wall friction term was large. The liquid film thickness δ_f could be expressed by the previously proposed correlation. For the rough film (RF) due to flooding at the bottom end in the region of high J_G, no significant difference was observed for f_w and f_i between D = 40 and 60 mm. We confirmed that CCFL characteristics at the lower end (CCFL-L) with R/S could be expressed by the Kutateladze parameters in the range of D = 40-60 mm and the characteristics were those for large diameters in the region of D ≥ 40 mm.