The catalytic activity for CO oxidation has been studied for samples of the solid-solution series LaCo1-tCrtO3, and NdCoO3 for comparison. The catalytic activity over LaCo1-tCrtO3 generally decreases with increasing chromium content. For samples with t = 0.70 and 0.80, distinct activity changes occur during the reaction, for t = 0.80 representing a permanent deactivation. Samples of LaCo1-tCrtO3 were also studied by XRD, TPR, TG and XPS. Variations in catalytic activity were compared with variations in structural, physical and chemical properties. A rough correlation was found between the starting temperature for reduction during TPR and the temperature required for 5% CO conversion. Furthermore, the activity pattern at 600 K follows the atom percentage of surface oxygen species as seen by XPS. Possible surface reactions on LaCo1-tCrtO3 during the catalytic oxidation of CO are discussed.