Drilling fluid plays many important roles in drilling operations of oil and gas wells. Research on application of nanoparticles in drilling fluid to combat several challenges has gained attention in recent years. In this study, we report experimental results of applications of copper oxide/polyacrylamide nanocomposite as water-based drilling fluid additive. Nanocomposite was synthesized with solution polymerization process and characterized with fourier-transform infrared spectroscopy, field emission scanning electron microscopy, and dynamic light scattering. The synthesized nanocomposite was added into water-based drilling fluid with different concentration and improvement of rheological, filtration and thermal conductivity were monitored through standard methods for both deionized water and salty water. A comprehensive procedure is proposed for synthesis and application of nanocomposite in drilling fluid. The results showed highly improvement in drilling fluid viscosity. Fluid filtration (fluid loss) volume and filter cake thickness were reduced significantly. Smoother and less porous filter cake obtained with nanocomposite additive. Thermal conductivity was increased substantially. Nanocomposite additive was more effective in deionized water-based drilling fluid for filtration and rheological properties while in salty water thermal conductivity was improved more than that for deionized base drilling fluid. (C) 2019 Elsevier B.V. All rights reserved.