In this study, the thermoelectric properties of boron phosphide-filled polyaniline (PANI/BP) composites were examined. The composites containing different weight ratios of BP such as 0.5%, 1%, 3%, 5%, 7%, and 10% were prepared by the in situ oxidative chemical polymerization of aniline. From the electrical conductivity measurements, it was observed that the electrical conductivity of the pure PANI increased from 2.93 to 117 Scm−1 with the addition of 7% BP. Seebeck coefficient measurements showed that all the composites have negative Seebeck coefficients which is the characteristics of n-type conductors. The largest Seebeck coefficient was found as − 78.8 µVK−1 from the composite containing 0.5% BP. Furthermore, the highest power factor was calculated as 45.3 µWm−1 K−2 indicating that BP is a promising additive for the thermoelectric composites.