A fan frame has at least one protrudent connector and at least one recessed connector. The at least one protrudent connector is formed on a corner of a surface of the fan frame. The at least one recessed connector is formed on another corner of the same surface of the fan frame, opposite to the at least one protrudent connector and corresponding to the at least one protrudent connector of another same fan frame. Two fan frames can be securely connected against each other by engaging corresponding protrudent and recessed connectors.