AbstractThe catalytic activities in the hydrolysis of 4‐nitro‐ and 2,4‐dinitrophenyl acetate were determined for a polymer of 3‐(4‐imidazolyl)‐2‐isocyanopropanoic acid (1a) and of 2‐(4‐imidazolyl)‐1‐isocyanoethane (1b). A detailed kinetic analysis has been performed. The reaction starts with acylation of the imidazole groups followed by deacylation. With excess of substrate the second step is rate‐determining and the system shows burst kinetics behaviour. The rate of acylation of 1a can be analyzed by a two term equation; the major term involves the COOH groups. A transition state is proposed in which COOH stabilizes the negative charge developing on carbonyl oxygen. This system is approximately 400 times more active than e.g. histidine. The data for 1b reveal that the polymer imidazole groups are approximately six times more active than e.g. the imidazole group of histamine. This phenomenon is ascribed to a cooperative effect of the polymer imidazoles.The deacylation is general base catalysed. Its rate constants are almost equal to those of acetylimidazole.For comparison, the hydrolysis of the charged substrates 4‐acetoxy‐3‐nitrobenzoic acid anion and 3‐acetoxy‐N,N,N‐trimethylanilinium iodide by 1a and 1b has been included.