Abstract: In-hospital neutron irradiator (IHNI) was specially designed for boron neutron capture therapy (BNCT).On the both sides of the reactor core, there are two neutron beams. One is thermal neutron beam, and the other opposite to the thermal beam, is epithermal neutron beam. A small thermal neutron beam is specially designed for the measurement of blood boron concentration by the prompt gamma neutron activation analysis (PGNAA). The six experiments were completed during startup. The results show that the maximum continuous operation time at full power is 12 h, and the final excess reactivity is 4.2 mk. The radiation dose rates at different rooms meet the designed requirement. When the positive reactivity with 4.2 mk is inserted into the reactor suddenly, the power will increase to peak power, and then, it will turn to the normal value due to the negative temperature effect, and the release result of reactivity shows the inherent safety of IHNI.