Cu oxide nanoparticles were formed by reacting with Polyamic acid (PAA) with Cu during imidization. In this paper, we investigated the effect of holding time during curing on the Cu oxide nanoparticle formation. Cu thin films were deposited on SiO2/Si substrates by thermal evaporation. Polyamic acid was then spin-coated on the Cu thin film. The polyamic acid films were soft-baked at 135°C for 30 minutes and thermally cured at 350°C with various holding time in a nitrogen atmosphere. The size of the Cu2O nanoparticles formed in the polyimide (PI) matrix increased as the holding time increased. The size and distribution of Cu oxide particles were characterized using Transmission Electron Microscope (TEM). The degree of imidization of PI also increased proportional to the increase in holding time. The degree of PI imidization was analyzed by Infrared (IR) spectroscopy. Very uniform Cu2O particles less than 5 nm in size with particle density greater than 2×1012/cm2 were fabricated by controlling the holding time during curing.