Studies were made on the reactivity with water of the following complexes: 4,4,4-tri(cobalt-tricarbonyl) butyric acid (I), butenolidyl-dicobalt-heptacarbonyl (II) and 4,4,4-tri(cobalt-tricarbonyl) crotonic acid (III). The organic products directly deriving from the degradation of the examined complexes were respectively: glutaric acid from complex (I); $\Delta^{\alpha,\beta}$-butenolide from complex (II); vinyl acetic and glutaconic acids from complex (III); However, during the reactions carried out and in function of the operating conditions, complex (II) can also give complexes (I) and (III); and complex (III) can also produce complex (I). Therefore, the organic products that can be obtained from any single run, can all be those corresponding to the degradation of the relating cobalt-carbonyl complexes. On the contrary, no direct hydrolysis reaction was observed on the examined complexes.