We have developed a new real-time neutron detector, which is able to measure a direct neutron beam of boron neutron capture therapy. The detector consists of both a 40-μm-thick pn diode and around 0.09-μm-thick LiF neutron converter. Experimental results indicate that this neutron detector can measure neutron flux up to 1 × 109 (cm-2 s-1), separately from gamma rays around 500 mGy/h. The measured depth distribution of neutron flux in an acrylic block is in agreement with the activation results of gold.