Friction loss of rough wall tubes is significant for design of marine piping system. The author has performed an experimental study on friction loss of air-water two phase flow with vertical rough wall test tubes. The objective of the work is to obtain an empirical equation of friction loss of two phase flow in rough wall tube with a new arrangement method. Three empirical equations of friction loss have been obtained in the region of gas quality x=10^-5-10^-2. The friction loss of two phase flow in rough wall tube is arranged well with a factor F=Re_l Kⁿ X^m⋅ Re_l is Reynolds Number and K is a wall roughness factor. The exponent m is 1/4 and n is 1/3, 1/9 and 1/46 in the range of x=10^-3-10^-2, 10^-4-10^-3 and 10^-5-10^-4, respectively. The result of Chisholm who used horizontal rough wall tubes is also arranged well with the factor. The effect of gas flow rate on the friction loss of two phase flow in rough wall tube is almost as same as that in smooth wall tube.