The 2v3 bands of 10BF3 and 11BF3 have been studied at high resolution. The experimental values of the Coriolis coefficient ζ33 are 0.7808 ± 0.0036 for 10BF3 and 0.7438 ± 0.0047 for 11BF3. The BF bond length is found to be 1.3102 ± 0.0012 Å. The Coriolis coefficients have been used to fix the E′ species symmetry force constants.