The speed of sound in hexane and heptane (mass purity > 0.990, GC) was measured using the Brillouin light scattering method at T = (300.15 to 506.15) K for hexane, (302.15 to 536.15) K for heptane), and p = (1.0 to 8.5) MPa, including saturated liquid, saturated vapor, and compressed liquid. The expanded relative uncertainty (k = 2) of the speed of sound was estimated to be less than 1.0% over the whole investigated range of states. Polynomial representations for the speed of sound in hexane and heptane were fitted to the experimental results. A comparison of the speed of sound data with the correlation shows that, for hexane, the AAD is 0.67% for the saturated liquid, 0.36% for the saturated vapor and 0.57% for the compressed liquid respectively, and for heptane, the AAD is 0.46% for the saturated liquid, 0.38% for the saturated vapor and 0.41% for the compressed liquid, respectively.