The OH radical dissociation has been studied behind shock waves in the temperature range of 2950-3700 K at total pressures of about 220-310 kPa by Atomic Resonance Absorption Spectroscopy using mixtures of H-2 and O-2 highly diluted in At. The OH decomposition was followed by monitoring the time dependent O concentration in the post shock reaction zone. In our experimental conditions this reaction is very sensitive to O-atom profiles. The rate constant k(-2) of the termolecular recombination reaction between H, O and Ar as collision partner was calculated from OH dissociation rate constant k(2) measurements and the equilibrium constant. The results expressed in the simple Arrhenius form are: k(2) = 1.2 x 10(15) exp(-48100/T) cm(3) mol(-1) s(-1) k(-2) = 6.75 x 10(18) T-1 cm(6) mol(-2) s(-1) with an uncertainty of +/- 30%, which are in good agreement with the estimate of Tsang and Hampson in 1986. No experimental results were reported by earlier investigators.