Abstract: The residence time distribution for laminar flow of non-Newtonian Casson fluids in a tubular reactor was analysed theoretically,and the analysis expressions were derived for the residence time distribution density function in the Casson laminar flow reactor.Based on the residence time distribution density function derived, equations to calculate the product distribution for simple series reactions in an isothermal tubular reactor were presented. The conditions which must be satisfied for maximizing intermediate product yield were derived. Computation of optimal Dahmkohler number, optimal conversion and maximum possible yield of intermediate product was carried out. By using these calculated results, design charts which show quantitatively how the reaction rate constant ratio and the parameter of Casson laminar flow model affect optimal product distribution and optimal Dahmkohler number were obtained.Also,correlated diagrams and correlations which show the influence of parameter of Casson laminar flow model on optimal feed rate and optimal reactor volume were given. These diagrams and correlations are useful for engineering design.