Recently, the synthesis of metal nanocrystallites using plant extracts has received much attention due to its low cost and compatibility with the environment. In this research, copper nanocrystallites were synthesized using hawthorn extract. The formation of copper nanocrystallites was observed by changing the color of the solution. Synthesized copper nanocrystallites were investigated by techniques such as: Ultraviolet-Visible Spectroscopy (UV-Vis), Scanning Electron Microscope (SEM), Fourier Transform-Infrared Spectroscopy (FTIR), Energy Dispersion Spectroscopy (EDX) and X-ray Diffraction Spectroscopy (XRD). In the UV-Vis spectrum, a dominant absorption peak at 552 nm wavelength was observed, which was related to copper nanocrystallites. In the images taken from SEM, it was found that the nanocrystallites are nearly spherical in shape and their average size on the surface of the sample was about 61-85 nm. Parallerly, in the investigation of antibacterial properties, synthesized nanocrystallites showed better antibacterial activity against Gramnegative bacteria (Escherichia coli) respect to other bacteria in the present work. The obtained results show that hawthorn extract can be used for the synthesis of copper nanocrystallites.