The rate of oxidation of thiamine ( Vitamin B, ) by Hg(II) ion in basic medium (pH=12.2) has  been  studied The   concentration of [OH']and Hg(II) were kept  constant by using  0.20M phosphate buffer and 2.0×10-3M Hg(II).  The initial rate of formation of the only product   of thiochrome was  followed spectrophotometrically at h   = 350 nm for the first 2-3 minutes  The reaction has  been studied  in the temperature range of  279 K  to 314.4 K.  The reaction is pseudo-first  order with  respect to thiamine .Different kinetics and thermodynamics parameters such as rate costants, activation energy, enthalpy of activation, entropy of activation and   Gibbs   energy  of   activation of  the  reaction were   reported. Various concentrations of thiamine  were   successfully found   by  measuring  there  initial  rates  in   different synthetic mixtures containing other foreign species.