Over the past few years,environment-friendly green synthetic methods for metal nanoparticles(NPs)have received considerable attention.The use of plant extracts is considered as potential for the biosynthesis of metal NPs due to its easier obtainment,cheap accessibility to industrial scale-up and high biosecurity.Herein,with the aqueous leaf extract of barley leaves as the template,we reported a rapid,single step,cost-effective and eco-friendly synthetic route to prepare new gold nanoparticles(BL-Au NPs).Significantly,except for the key role as the reducing,barley leaves was further utilized as the capping agent that ensure the stability of the BL-Au NPs.The characterization results of TEM,FTIR and UV-vis indicated that the gold nanoparticles coated with barley leaves extract were successfully synthesized.In vitro and zebra fish toxicity and stability assays demonstrated its good biocompatibility and high colloidal stability.The CT images in vitro demonstrated that the constructed BL-Au NPs possessed superiority in X-ray attenuation ability compared to clinically commonly used iodinated small molecular contrast agent.And BL-Au NPs can be used as contrast agent for effective CT imaging of zebra fish model.These results suggest the potential utility of BL-Au NPs as a CT imaging contrast agent in clinical CT imaging based diagnosis.