Various solutions for physical downlink control channel (PDCCH) monitoring configuration for carrier aggregation (CA) with respect to user equipment and network apparatus in mobile communications are described. An apparatus may transmit a capability report to indicate a plurality of monitoring combinations of PDCCH monitoring capabilities to a network node. The apparatus may receive a monitoring combination configured by the network node based on the capability report. The apparatus may determine a monitoring budget by using the configured monitoring combination. The apparatus may perform a PDCCH monitoring according to the monitoring budget.