A graphite ore with ultra-large flakes (ULFG) found in China (Wulate County, Inner Mongolia Autonomous Region, China), was first jaw-crushed and pneumatically separated to remove rocks, before being subjected to two froth-flotations and finally leached with NaOH and HCl to a purity of 99.9%. The purified ULFG was used to prepare exfoliated graphite by a combined chemical intercalation and rapid heating method and the latter was rolled into flexible graphite sheets of different densities. Results show that the beneficiation and purification methods preserve the graphite crystallites. The purified ULFG has a high degree of graphitization (99.9%). The volume of the ULFG-based exfoliated graphite is more than 400 mL/g, and some randomly selected individual exfoliated graphite particles are larger than 40 mm. A ULFG-based flexible graphite sheet with a density of 1.8 g/cm³ shows an excellent electrical conductivity of 2.78×10⁵ S/m.