In the fathomable design of ultra low current mode circuit (UCMC), circuit for on-chip measurement and monitoring of pico-ampere current is in high demand, not only for its simplicity in structure and cheapness in price, but also for its high measure accuracy and process tolerance. In this paper, on-chip ultra low current measurement methodologies based on hazard free sawtooth oscillator whose average leakage is as small as 1.61pA (at 27°C) have been proposed and verified using SMIC models of 0.18μm CMOS process. Meanwhile, capacitance and leakage calibration techniques for high precision on-chip ultra low current monitoring are also characterized and discussed.