The Henry's law constants for aqueous solutions of hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid were measured over the temperature range 278¿-293¿K. These determinations were made by measuring the vapor pressure of the peroxide in gas stream of nitrogen or air that was in equilibrium with a solution of known peroxide concentration. The aqueous phase concentrations ranged from 5 ¿ 10-5 M to 5 ¿ 10-3 M for hydrogen peroxide, and from 1 ¿ 10-6 M to 1 ¿ 10-4 M for methylhydroperoxide and peroxyacetic acid. In all cases, Henry's law was obeyed over the concentration range investigated. The temperature dependence of the Henry's law constant is expressed by KH = e<A/T-B>, where KH is in the units of molar concentration per atm, and T is in degrees Kelvin. The coefficients' values are A = 6621, B = 11.00 for hydrogen peroxide; A = 5607, B =13.41 for methylhydroperoxide; and A = 6171, B = 14.55 for peroxyacetic acid. The experimental errors on KH at the 95% confidence level are ¿8.3% for hydrogen peroxide, ¿11% for methylhydroperoxide, and ¿17% for peroxyacetic acid. In addition, the Henry's law behavior of hydrogen peroxide in aqueous solutions of sulfuric acid and ammonium sulfate was investigated. The Henry's law constant of hydrogen peroxide decrease with increasing sulfuric acid concentration and increased with increasing ammonium sulfate concentration.