An ultra-high performance liquid chromatography (UHPLC) with UV detection method was developed for the fast quantitation of the most represented and biologically important green tea catechins and caffeine. UHPLC system was equipped with C18 analytical column (50 mm × 2.1 mm, 1.8 μm), utilizing a mobile phase composed of pH 2.5 triethanolamine phosphate buffer (0.1 M) and acetonitrile in a gradient elution mode; under these conditions six major catechins and caffeine were separated in a 3 min run. The method was fully validated in terms of precision, detection and quantification limits, linearity, accuracy, and it was applied to the identification and quantification of catechins and caffeine present in green tea infusions. In particular, commercially available green tea leaves samples of different geographical origin (Sencha, Ceylon Green and Lung Ching) were used for infusion preparations (water at 85 °C for 15 min). The selectivity of the developed UHPLC method was confirmed by comparison with UHPLC–MS/MS analysis. The recovery of the main six catechins and caffeine on the three analyzed commercial tea samples ranged from 94 to 108% (n = 3). Limits of detection (LOD) were comprised in the range 0.1–0.4 μg mL−1. An orthogonal micellar electrokinetic (MEKC) method was applied for comparative purposes on selectivity and quantitative data. The combined use of the results obtained by the two techniques allowed for a fast confirmation on quantitative characterization of commercial samples.