A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative-tone photosensitive polyimide (PSPI) precursor. 3-Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m(-1) K(-1) for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 mu m were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass-transition temperatures were above 360 degrees C, and the thermal decomposition temperatures were over 460 degrees C. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 916-922, 2011