Hybrid K-edge densitometer (HKED) is used for concentration measurement of U, Pu and minor actinides in liquid solution samples. We propose a multi-turn smallsize energy-recovery linac (ERL) to produce laserCompton scattered X-rays for the HKED. The X-rays with good monochromaticity and energy tunability allow measurement of nuclear materials faster than the existing HKED systems based on X-ray tubes. The ERL energy is 85 MeV to produce 130-keV X-rays. In the present design, we adopt a racetrack configuration, in which electrons are accelerated six times by L-band superconducting linac and decelerated six times for the energy recovery. Design and expected performance of the ERL-HKED are presented.