Properties of the scintillator bars are very important to the goal of 90 ps time resolution of the TOF detec-tor on BESIII.The mechanical sizes were measured.The scintillator bars were piled up to measure the effective at-tenuation length and relative light output by cosmic rays.The positions hit by cosmic rays were deduced by time in-formation acquired from the PMTs at the two ends of the scintillators.The results show that the scintillators is very good in quality for BESIII TOF.