The kinetics of the reaction of (7-amino-8-methyl-phenothiazin-3-ylidene)-dimethyl-ammonium chloride (herein referred to as TB) by Perchlorate ion has been studied at 30 ± 1°C, [H+] = 1 x 10-2 mol dm-3 and ionic strength (I) = 0.5 mol dm-3 (NaCl). The reaction is first order in both the oxidant and the reductant. The redox reaction displayed a 1:1 stoichiometry and obeys the rate law: -  = (a + b [H+]) [TB+][ClO4 -] Where a = 3.1 x 10-2 dm3 mol-1 s-1, and b = 1.63 x 103 dm3 mol-1 s-1 The second-order rate constant increases with increase in acid concentration. It decreases with increasein ionic strength and dielectric constant. Added anions inhibited the reaction rate while spectroscopic investigation and Michaelis-Menten plot showed no evidence of intermediate complex formation in the course of the reaction. A plausible mechanism has been proposed for the reaction.