Abstract: A spectrum sharing scheme for a pair of secondary users co-existing with multiple primary users was proposed. The primary users exploit the limited feedback of channel quality information (CQI) to allocate their transmission power and rate. By overhearing the limited feedback of primary CQI, the secondary user accessed the channel with proper transmission power and rate while causing interference to the primary users and so the rate loss of the primary system. Under the primary rate loss constraint, the optimal transmit power and transmission rate for the secondary was obtained to maximize the secondary user throughput. Numerical results show that, with only 3 or 4 bits of feedback to each primary user, the effective throughput of the secondary system is comparable to the case with both primary and secondary transmitters having the perfect CQI of the primary link. The simulation results demonstrate that the proposed spectrum sharing scheme can meet the primary rate loss constraint.