The kinetics of thermal degradation of thiamine and surface colour (lightness measured as Hunter L-value) in canned white tuna were determined using an unsteady-state experimental procedure. Kinetic parameters were calculated by weighted non-linear regression considering a first-order kinetic model with a dependence of the kinetic coefficient (D) with temperature of the Thermal Death Time (TDT) type. Mass-average retentions of thiamine were calculated using a mathematical model which takes into account the non-uniform and unsteady distribution of temperature inside the container during thermal processing. The high correlation obtained between the predicted and the observed retention values and the small confidence intervals found for the kinetic parameters indicate a high statistical reliability. The kinetic model thus determined permits the simulation and optimization of the process resulting in a better quality of the final product.