A low noise precision operational amplifier was designed in a 40 V bipolar process, which was used in high precision and high resolution systems. The whole structure and operation mechanism of the operational amplifier were introduced. The key design techniques of operational amplifier such as reduced input bias current, reduced input offset voltage and frequency compensation were analyzed in detail. Then the operational amplifier was simulated with Spectre tool, and it was fabricated and verified. The tested results indicated that, under ±15 V power supplies, the device achieved an input bias current of 2 nA, an input offset voltage of 10 μV, a large signal voltage gain of 132 dB, a common mode reject ratio of 135 dB, and a power supply reject ratio of 130 dB. The circuit met the requirements of high precision, high resolution and low noise applications.