Catecholamines, generally including dopamine (DA), epinephrine (EP), and norepinephrine (NE), are important neurotransmitters and serve many central nervous system functions. In this work, a simple colorimetric method for the determination of the three catecholamines is developed. The proposed method is based on the fact that Ag⁺ could oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB) and induce a blue color solution corresponding to an absorption peak centered at 652 nm. However, the introduction of catecholamines could cause the reduction of oxTMB which results in the fading of the blue color quickly and a decrease of the absorbance at 652 nm. Based on this finding, we propose a method to quantitatively detect catecholamines with the help of UV-vis spectroscopy. The detection limit (S/N = 3) for DA, EP, and NE is 50 nM, 100 nM, and 150 nM, respectively. More importantly, this method is simple, fast and without the use of complicated nanomaterials. This method has been successfully applied to the detection of catecholamines in pharmaceutical samples.