In the present work, Al2O3-SiO2-B2O3 composite nanofibers with mullite-type structure were prepared using electrospinning technique. The microstructure and elastic modulus of the composite nanofibers obtained at elevated temperatures were studied. The results showed that Al4B2O9 phase formed at 900 degrees C and then transformed to Al18B4O33 at 1100 degrees C. Mullite was also detected in the nanofibers prepared at 1100 degrees C. Amorphous SiO2 existed in all samples even the calcination temperature reached up to 1400 degrees C. The continuous and uniform structure of the composite nanofibers was kept after calcining at different temperatures, while rougher surface was evident due to the growth of the grain caused by the elevated temperature. An increase of elastic modulus of the samples from 9.47 +/- 1.91 GPa to 27.30 +/- 2.61 GPa was observed when calcination temperatures increased from 800 degrees C to 1400 degrees C.