Micrometer boron nitride/polyamide acid (mBN/PAA) compound was firstly fabricated via in-situ polymerization, performed to obtain the mBN/PAA electrospun fibers by electrospinning technology, finally to fabricate the dielectric thermally conductive mBN/polyimide (mBN/PI) composites via thermal-imidization followed by hot press method. The obtained mBN/131 composite with 30 wt% mBN presents relatively highly thermally conductive coefficient (lambda), excellent dielectric constant (epsilon) & dielectric loss tangent (tan delta), and extremely outstanding thermal stability, lambda of 0.696 W/m K, epsilon of 3.77, tan delta of 0.007, THeat-resisrance index (T-HRI) of 279 degrees C and glass transition temperature (T-g) of 240 degrees C, which presents a great potential for packaging in integration and miniaturization of microelectronic devices. (C) 2016 Elsevier Ltd. All rights reserved.