Abstract: A GPS disciplined rubidium oscillator is designed for timing application. After disciplined, the rubidium oscillator outputs a second signal which is real-time synchronized to the second signal of the GPS receiver. In the same time, the time difference between the rubidium oscillator and the GPS receiver is processed to calibrate the frequency of the rubidium oscillator through a PI controller. The time difference is less than 10ns，the frequency difference is less than 1E-12/day between two GPS disciplined rubidium oscillator.After a dedicated GPS signal processing board and a particular GPS receiver is used, the time difference can be limited to 5ns.

Key words: Time, Frequency, Rubidium oscillator, GPS