Green and efficient mass production of graphene sheets with high quality and electrical conductivity is intriguing for both academic scientists and industry. Among numerous production methods suffering from complexity or harsh chemical media, direct and high-yield exfoliation of graphite in water seems to be the best choice. In this study, efforts were made to prepare high-quality and stable graphene dispersions with the highest possible concentrations through an ultrasound-assisted liquid-phase exfoliation (LPE) in water directly from two types of natural graphites. The rigorous structural, morphological and electrical analyses were conducted on both graphite and graphene samples to quantitatively identify the effect of graphite sources on the LPE yield and the quality of the graphene nanosheets produced in the presence of an ionic surfactant. The results obtained by TEM, AFM, XRD and Raman spectroscopy indicated the successful and efficient production of single and few layer graphene sheets with the remarkable concentration of 3.18mg.ml-1 in water. Moreover, the results signified that the structural quality, electrical conductivity and production yield of the graphene layers undoubtedly depend on the structural properties of graphite source. In fact, the graphite source greatly influences the final properties and potential applications of the produced graphene layer and the results are so important for the future graphene industry.