Abstract: Cymbopogon citratus (lemongrass) leaves and/or infusion are commonly consumed as a beverage or as an herb in several cuisines worldwide. It is also used in traditional medicine for the treatment of several pathologic conditions, such as peptic ulcers, inflammatory conditions and cancer. Recent studies revealed the crucial role of the phenolic compounds of the infusion bioactivity as anti-inflammatory and antineoplasic, particularly attributed to flavonoids. A High-Performance Liquid Chromatography-Diode-Array Detector (HPLC-DAD) method was developed, for the first time, for the simultaneous quantification of phenolic compounds in Cymbopogon citratus polar extracts, which seem to be the main contributors to the antioxidant effects of this herb. The separation was performed on a Spherisorb S5 ODS-2 column (250×4.6 mm i.d; particle size, 5 μm), using a methanol: aqueous formic acid (5%, v/v) gradient as the mobile phase, with a flow of 1 mL min–1. The detection was achieved with a DAD detector and the chromatographic profiles were registered at 280 nm. The developed method was validated according to the Food and Drug Administration (FDA) recommendations. Good linearity was observed within a wide concentration range. The developed method is simple, precise at the intra-day and inter-day levels and accurate with very good recovery percentages. Phenolic acids and flavonoids, including luteolin 6-C-glucosyl-8-C-arabinoside, luteolin 6-C-glucoside, luteolin 7-O-glucoside, luteolin 7-O-neohesperidoside, luteolin 6-C-arabinosyl-2"-O-rhamnoside and luteolin 2"-O-rhamnosyl-C-(6-deoxy-ribo-hexos-3-ulosyl) were successfully quantified in leaves infusion of C. citratus using the developed HPLC method. This data may be of great interest for the food supplement and pharmaceutical industries.