Laminar flame speeds of n-butane/dimethyl ether (DME)-air mixtures were first measured using the outwardly expanding spherical flame and high-speed schlieren photography over a wide range of equivalence ratios, nitrogen dilution ratios, and DME blending ratios at elevated temperatures and pressures. The measured flame speeds were compared to the calculated flame speeds with some representative chemical kinetic models. Results show that laminar flame speeds of n-butane/DME blends slightly increase with the increase of the DME blending ratio. Reaction pathway analysis was performed, and the effect of the DME blending ratio on the laminar flame speed was interpreted with the latest Aramco Mech 1.3 model. A correlation of the laminar flame speed of n-butane/DME blends as a function of the equivalence ratio, temperature, pressure, and DME blending ratio is provided.