This paper presents a sensitive electrochemical method for the determination of cysteamine (CA) using promazine hydrochloride-modified multi-wall carbon nanotubes carbon paste electrode (PrH/MWCNTs CPE). Because of the good electrochemical activity of MWCNTs and the acceptable performance of promazine hydrochloride (PrH) as an electrocatalytic mediator, the modified electrode significantly enhanced the sensitivity for the detection of CA in comparison to the bare carbon paste electrode (CPE). All chemical parameters such as pH of solution, concentration of PrH and kinetic parameters of the system were investigated. Linear sweep voltammetric (LSV) method was used to follow the electrocatalytic effect of CA on the current–potential response of PrH. Under optimum conditions, the obtained net peak current ∆I p(I sample − I blank) was linear with CA concentrations in two dynamic ranges of 2.0–346.5 μmol l−1 (∆I p = (0.0195 ± 0.0043)C CA + (0.7648 ± 0.0397) (r 2 = 0.9948)) and 346.5–1,912.5 μmol l−1 (∆I p = (0.0100 ± 0.0026)C CA + (3.8981 ± 0.0828) (r 2 = 0.9911)) with a detection limit of 0.8 μmol l−1. Finally, the PrH/MWCNTs CPE was successfully applied for the determination of CA in urine and drug samples with satisfactory results.