A simple method was introduced to determine the activities of activated carbon-supported palladium (Pd/AC) catalysts in the hydrogenation of cinnamic acid (CA). Catalytic transfer hydrogenation (CTH) of CA to hydrocinnamic acid (HCA) is a suitable reaction for this purpose. In order to detect the reaction completion, the simple Bayer's test is also a good alternative for the costly device test, for example, GC and HPLC. The ability of this method for accurate measurement of the catalyst activity is proven by comparing its results with data obtained from the catalytic hydrogenation (CH) reaction of CA to HCA. Four commercial 10% Pd/AC catalysts were used in which their characterizations are determined. The reliability of correlation between the obtained activities from catalysts in two CH and CTH reactions is confirmed by high and low values of the coefficient of determination (R-2 = 0.9895) and standard error (s = 2.84), respectively. It is indicated that there are some similarities between the mechanisms of these two reactions. Since their kinetics are very similar, the rates of both catalyzed reactions are zero-order. Here, we show that this method can measure the activity of Pd/AC catalysts in CH of CA as well as investigate the possible use of this method for the hydrogenation of other alkenes.