We investigate theoretically and compare optical properties of wurtzite and zinc-blende GaN/AIN quantum dots with heights, from 1.5 to 4.5 nm. The quantum dot size corresponds to the strong quantum confinement regime. It has been established that the built-in piezoelectric field at the GaN/AIN interface governs optical properties of wurtzite quantum dots while having a small effect on zinc-blende quantum,dots. The strain field strongly modifies the excitonic states in both wurtzite and zinc-blende GaN/AIN quantum dots. It has been shown that the radiative lifetime dependence on the quantum dot height is very different in the zinc-blende and wurtzite quantum dots. The excitonic optical properties of GaN/AIN quantum dots calculated using our model are in good agreement with available experimental data. Reported theoretical results for the optical spectra of GaN/AIN quantum dots can be used for interpretation of experimental data and optimization of the quantum dot structures for optoelectronic applications. (C) 2004 American Vacuum Society.