The kinetics of decarbonylation of pentacarbonyltechnetium halides TcX(CO)₅ (X = Cl, Br, I) in CCl₄ solution with the formation of dimers [TcX(CO)₄]₂ and of CO substitution in TcBr(CO)₅ by the solvent molecule in CH₃CN solution with the formation of the complex TcBr(CO)₃(CH₃CN)₂ was studied. In all the systems, the reaction is first-order with respect to the starting compound. It was concluded that the limiting step of the reaction is dissociation into the intermediate complex TcX(CO)₄ and CO molecule. The rate constants and activation energies of the reactions were determined.