In this paper, a CMOS oversampling delta sigma (Δ Σ) magnetic to digital converter (MDC) is proposed. In the MDC, the magnetic operational amplifier (MOP) combines with the switched capacitor (SC) Δ Σ modulator, and converts the external magnetic field into digital form. Simulation and measurement results indicate that the average digital output versus the applied magnetic field is quite linear. The prototype circuit was fabricated in a 0.5 μm CMOS DPDM process. The circuit operates at a 5 V supply voltage and the sampling rate of 2.5 MHz. The maximum signal range of the converter is at least ±100 mT and the resolution can reach as small as 1 mT. The gain error within ±100 mT is less than 3%. The conversion gain is 1.327 mv/mT and the power consumption is 49.3 mW.