The present paper reports on spectroscopic investigation of copigmentation effect of sinapic acid on the malvin molecule. A reaction of copigmentation was investigated by the use of UV-Vis absorption spectra in the whole range of acidic and moderately acidic buffered aqueous solutions (pH range 1.0-6.0). It was observed that the ratio (A-A0)/A0, as a good measure of the copigment effect, has its maximum value at pH 3.6. The influences of the pH of the medium, molecular concentration, and temperature were investigated. The reaction was thermodynamically defined in terms of deltaH0, deltaG0 and deltaS0 values.