Gasoline is so volatile that a large amount of vapor is quickly evolved from the gasoline surface. If motor gasoline is spilt for the purpose of arson or leaked out extensively on a floor by an accident, the gasoline vapor diffused into air and a flammable gas zone is formed in the immediate surroundings. In these cases, it is necessary to clarify the concentration distribution of generated gasoline vapor in order to evaluate fire hazard. On the other hand, flash points of kerosene and light oil are higher than room temperature, and evaporation characteristics of these fuels are different from that of gasoline. Therefore, kerosene and light oil addition to gasoline will decrease vapor pressure and ignitability of gasoline. The aim of this paper is to accurately predict the evaporation and diffusion behavior of gasoline mixed with low-volatile fuel such as kerosene and light oil. We assumed that the components originated in gasoline were selectively volatilized from gasoline mixed with low-volatile fuel and governed by presented prediction models of vapor pressure and evaporation rate of the mixed gasoline. Using the assumption, a prediction model of concentration distribution of combustible vapor over spilt mixed gasoline was derived. To verify the model experimentally, ignition tests of combustible vapor over the mixed gasoline were conducted.