The refractive indices n of pure formamide, 1-butanol, 2-butanol, 1,3-butanediol, 1,4-butanediol, and those of their binary mixtures, with formamide as the common component, covering the whole composition range, have been measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K. From the experimental data, the deviations in refractive index (Delta n) have been calculated. The variation of Delta n with composition and temperature has been discussed. The extent of deviations in refractive indices for these mixtures follows the sequence 1-butanol > 2-butanol > 1,3-butanediol > 1,4-butanediol, and An decreases with an increase in temperature.