Abstract The apparent first-order rate constant corresponding to the hydrolysis of niacinamide has been determined over the pH range 0.4–11.3 in purely aqueous solutions at 89.4. Although the pH-rate profile shows a minimum between pH 4 and 6, the reaction velocity is relatively slow over the usual pharmaceutical range. Surprisingly, the second-order proton catalyzed rate constants for the free vitamin and its protonated form appear to be roughly the same. The hydrolytic reaction appears to be subject to both general acid and general base catalysis.