The solubility of HBr in 54 to 72 wt % sulfuric acid at low temperatures (200 to 240 K) was measured using two different experimental techniques. In the first, the time dependence of the uptake coefficient of HBr was measured in a Knudsen cell reactor and analyzed to give the effective Henry's law coefficient. In the second, equilibrium vapor pressures of HBr (gas) over solutions containing known concentrations of HBr (dissolved) were measured. The two techniques were in good agreement Typical values of the effective Henry's law coefficient at 220 K were 1.5×107 M/atm for 54 wt %, 2.2 × 106 M/atm for 60 wt %, 1.5×105 M/atm for 66 wt %, and 8.5×103 M/atm for 72 wt % sulfuric acid. The measured solubilities combined with the stratospheric gas phase concentration of HBr indicate that very little HBr will be dissolved in stratospheric sulfate aerosol particles.