The effect of reaction temperature on catalyst deactivation during hydroprocessing of Maya heavy crude oil was studied. Experiments were carried out in a fixed-bed pilot plant at constant pressure, hydrogen-to-oil ratio, and space-velocity. Reaction temperature during 1120 h time-on-stream was varied from 400 to 430 degreesC. Catalyst deactivation was monitored by the changes in asphaltenes, sulfur, metals (V and Ni), and Rambottom carbon contents in the hydrotreated products. Fresh and spent catalysts were characterized by textural properties, metals, and carbon contents, and scanning electron microscopy. Coke and metals depositions were around 18.5 and 25%, respectively.