In the usual manner the relation between exposure and density, and some values of photographic materials derived from this relation are obtained graphically. The authors attempted to obtain these calculatively by using mathematical models. Three mathematical models were established for photographic characteristic curve. After the numerical analysis of parameters utilized in three models density values were calculated from values of parameters and were compared with density values obtained by experiment. Consequently it was found that a model gave satisfied approximation for most of photographic characteristic curves. Calculatively obtained values of sensitivity speed, γ and contrast index from parameters were neary equal to graphically obtained values.