In present study electrografting of the in situ generated 3‐carboxy‐1,2,4‐triazoldiazonium chloride on the Au disk electrode have been studied. The electrode film thickness differences between electrodeposited due to the aryl radical structure 3‐carboxy‐1,2,4‐triazoldiazonium chloride and 4‐carboxyphenyldiazonium salt was shown. The mechanism of 3‐carboxy‐1,2,4‐triazoldiazonium chloride electrografting has been proposed. 4‐nitroanilin was used to investigate the carbodiimide crosslinking capacity. It was established that electrodeposited films are suitable for carbodiimide crosslinking but the reaction proceed only on the “external” electrografted layer. Under the chosen optimal parameters, the label‐free electrochemical immunosensor have been developed. 3‐carboxy‐1,2,4‐triazoldiazonium chloride electrografting provided improvement of analytical characteristics in respect to electrodeposited 4‐carboxyphenyldiazonium salt. The linear range for carcinoembryonic antigen (CEA) detection is 10–104 ng ⋅ ml−1, the limit of detection estimated as 0.2 ng ⋅ ml−1. The developed immunosensor is stable during 30 day′s storage and selective against excess of bovine serum albumin as an interfering reagent.