Abstract: In GPS/GLONASS satellite clock estimation, GLONASS code inter-frequency biases (IFB) can not be assimilated into the receiver clock parameters due to the discrepancy of GLONASS frequencies, which is partly involved in the GLONASS satellite clock estimates. In order to separate the GLONASS IFBs and the satellite clock estimates effectually, an approach for real-time GPS/GLONASS satellite clock estimation with multiple inter-system and inter-frequency bias (ISFB) parameters and additional restriction is proposed. The estimated satellite clocks and real-time precise point positioning results are then evaluated. The results show that ignoring GLONASS code IFBs could dramatically degrade the GLONASS satellite clock accuracy. The new approach can efficiently avoid the adverse impact of GLONASS code IFBs on satellite clock estimates. Compared with the ESA final satellite clock products, the average RMS of clock biases are less than 0.2 ns for GPS and 0.3 ns for GLONASS respectively. RT-PPP experiments were conducted with different session lengths. The 3D positioning accuracy of RT-PPP using the estimated satellite clocks was better than 10 cm for GPS-only and combined GPS/GLONASS modes, 15 cm for GLONASS-only mode with 2-h observations, and better than 5 cm for all the three modes with 24-h observations.