Laminar combustion characteristics of 2,5-dimethylfuran (DMF)/iso-octane/air/diluent (15% N-2/85% CO2) mixtures at atmospheric pressure and the initial temperature of 393 K were studied using the outwardly propagating spherical flame and high speed schlieren photography. Effects of DMF concentration in the fuel mixture and dilution ratio on flame properties were investigated, such as laminar flame speed, adiabatic temperature, effective Lewis number, and laminar flame thickness. Results show that laminar flame speed varied little, while the flame instability was slightly promoted as DMF concentration in the blends is increased. For all the fuels at fixed equivalence ratio, flame front morphology showed that the flame stability was enhanced with increasing dilution ratio. In addition, a linear relationship between the normalized laminar flame speed and the dilution ratio was found and an empirical formula was proposed for all the four different fuels at different equivalence ratios.