Malbec is a wine grape variety that is now mainly produced in Mendoza and considered to be the emblematic cultivar of Argentina. Forty-four phenolic compounds, including hydroxybenzoic and hydroxycinnamic acids and different flavonoids, were identified and quantified in 61 monovarietal Malbec wines from 11 geographical zones of Mendoza province, using a reversed phase high-performance liquid chromatography system coupled to a diode array detector (HPLC-DAD). Among non-flavonoids, gallic, cis-caftaric, trans-coutaric, and caffeic acids presented the higher concentrations in all of the samples, whereas trans-resveratrol glucoside was present at concentrations from 0.6 to 1.3 mg/L. For the flavonoids, (+)-catechin and (-)-epicatechin presented the higher concentrations among flavan-3-ols with a ratio (+)-catechin/(-)-epicatechin from 1.3 to 2.1. An astilbin derivative and quercetin presented the higher concentrations for flavonols, whereas malvidin-3-glucoside and its derivatives were the major anthocyanins. For the first time the phenolic composition of Malbec wines from Mendoza province has been characterized.