The flow boiling heat transfer is one of the common phenomenon happens in the industries. The micro-fin tubes are one of the geometries in enhancing heat transfer rate in boiling condition. The entropy generation analysis is presented with its formulation precisely to find best operating conditions in micro-fin tubes in terms of changing in geometry and flow conditions. This analysis shows important aspects of losses in fluid systems when boiling happens. The losses include thermal loss related to the heat transfer and hydraulic one related to the pressure drop. The relevant terms are described for both of these losses. The optimum tube diameter under specified conditions is found. The effect of different flow conditions such as mass velocity, inlet vapor quality on contribution of pressure drop and heat transfer in entropy generation is discussed. It is found that, there is a desirable conditions of fluid flow and micro-fin geometrical shape to reach the minimum of entropy generation.