We present the film bulk acoustic wave resonator-based ultramass-sensitive (FBAR-UMS) sensors in which their resonance characteristic improvements, mainly due to Bragg reflector (BR) annealing, favorably influence their performance factors. We fabricated two kinds of FBAR-UMS sensors, respectively, with nonannealed and annealed BRs (namely, nonannealed and annealed sensors) and investigated the effects of BR annealing on their performance factors by comparing their resonance frequency shift (-f(r)), measured before and after each mass loading (m). As a result, the annealed sensors showed much larger mass-loading effect and detectable mass range than the nonannealed ones.