Abstract: Cosmic rays interact with atmospheric atoms to generate high energy neutron radiation, which threats to the electronic system working in the atmospheric space environment. Neutron induced single event effect (SEE) occurring in the key component of an electronic system (i.e. microprocessor) seriously affects the system reliability. To study neutron induced SEE of microprocessor, a SEE monitoring system was designed for a 65 nm CMOS microprocessor from Texas Instruments (TI). The designed system has the ability to monitor SEE events that occur in tested microprocessor, and record corresponding voltage/current change in real time. To minimize the irradiation caused disturbance in monitoring system, it consists of two modules connected with 1 2 m communication line in irradiation room. One module carrying tested microprocessor is placed close to the neutron source. Another module acting as the master control board is placed as far away from the neutron source and is shielded against gamma ray with lead bricks. The upper order computer and 24 V direct current (DC) power supply are placed outside of the irradiation room. As a key component of the SEE monitoring system, the master control board is composed of microcontroller unit (MCU), power management chip, operating voltage/current monitor and peripheral circuit. The master control board is able to continuously monitor the internal operating status of the tested microprocessor and the voltage/current fluctuation. The 24 V input voltage is converted into two way power supplies. One is used for monitoring MCUs on master control board. Another one is used for the device under test (DUT). Operating voltage/current values are transferred to the upper order computer through a serial port. When the detected voltage or current values exceed set thresholds, monitoring MCU would cut off power supply through a relay. The SEE monitoring system was test using 14 MeV neutrons produced by D T reactions. Single event functional interrupt (SEFI) was observed in inter integrated circuit (I2C), internal flash memory, analog to digital converter (ADC), arithmetic and logic unit (ALU), controller area network (CAN), general purpose input/output (GPIO) and other units, while single event latch up (SEL) is not detected. I2C is found to be the most sensitive unit. Neutron induced SEE in I2C bus leads to a significant operating current drop. Moreover, when one of eight tested I2C buses is blocked under neutron irradiation, the following tests for rest I2C bus will turn out to be “FAIL” too, which implies the SEE might occur at the control part of I2C. The SEE cross section of tested microprocessor is evaluated to be 6 6×10-11 cm2 with the data of neutron fluence up to 3 5×1011 cm-2.