Nowadays, utilization of blended fuel in internal combustion engine is one of main topics in vehicle industries. The synergy effect will be highlighted when the potential of each fuel is employed and the engine performance will improve consequently.  In this research, the laminar flame speed of methane (main component of reference fuel for Natural gas) and isooctane (main component of reference fuel for gasoline) and their blended fuel, as an intrinsic characteristic of combustible mixtures is measured. Isooctane and methane with two volumetric fractions of 70% and 95% in blended are added in constant volume combustion chamber with partial pressure method in three temperature of 368, 408 and 448K and three pressure of 1, 2.5 and 5 bar. After filling the chamber in specified fuel air ratio, the mixture is ignited at the center of chamber and flame propagation is recorded with schlieren method. Laminar flame speed and Markstein length are calculated via post processing of flame images. Numerical simulation of flame speed is done using CHEMKIN code. Finally, a correlation based on temperature, pressure, equivalence ratio and methane mass fraction in blended fuel is proposed which predict the flame speed well.