The rate coefficient for reaction of OH with CH 2 C(CH 3 )C(O)OONO 2 (MPAN, peroxymethacrylic nitric anhydride), k 3 , has been determined using a relative rate technique. Consistent results were obtained with ethene and propene as the reference compound, and a rate coefficient of k 3 =(3.2+/-0.8)x10 - 1 1 cm 3 molecule - 1 s - 1 is reported at 275+/-3K. This value is about a factor of eight larger than the only previous report. A brief investigation of the products of the OH-initiated oxidation of MPAN and methacrylic acid (CH 2 C(CH 3 )COOH, an impurity in the MPAN sample but also a structural analog of MPAN) is also reported. Major products obtained in the case of methacrylic acid were CH 2 O and pyruvic acid (CH 3 C(O)C(O)OH), while CH 2 O, CO 2 , and possibly hydroxyacetone are observed in the case of MPAN. The atmospheric implications of the results are briefly discussed.