Transparent upconversion photoluminescent polyamide nanocomposites were fabricated via a facile in situ polycondensation method with interfacial chemistry modification employing polyacrylic acid-functionalized upconversion nanoparticles (UCNP-PAA) as fillers and transparent semiaromatic polyamides (SAPA) as host materials. The as-prepared UCNP-PAA could be dispersed uniformly in the polyamide salt solution and the SAPA chains can be grafted to the UCNP-PAA through condensation reactions. The grafted SAPA ligand on the surface of UCNP increases the compatibility between SAPA and UCNP, thus causing uniform dispersion of the UCNP in the polyamide nanocomposites and improving the transmittance of the polyamide nanocomposites. The obtained polyamide nanocomposites are transparent and show strong green upconversion photoluminescence. This work solved the problem of the dispersity of incorporated nanoparticles and improving the transparency of nanocomposites and, more importantly, endowed the traditional engineering plastic with upconversion photoluminescent properties which can be applied in three-dimensional displays and the related solar cell field in the future.