A laser Compton scattered γ-ray source based on a microtron is under development for non-destructive detection of nuclear material in cargo containers. In the detection system, we employ nuclear resonance fluorescence triggered by mono-energetic γ?-rays tuned at the resonance energy of nuclear material such as 235U. As a prototype, a 150-MeV microtron combined with a YAG laser to produce a 400-keV γ-ray is constructed at JAEA, where critical technologies are to be demonstrated for high-flux γ?-ray generation, 3x105 ph/s. We also design a microtron at higher energy, 220 MeV, to produce a 1744- keV γ?-ray, which is required for the detection of 235U. Copyright © 2011 by IPAC'11/EPS-AG.