In the analysis of biological samples, such as plasma or serum, the quantity of sample available is a critical parameter in most cases. A good approach is the use of the microelution SPE (μSPE) plates as sample pre-treatment technique in which the loaded sample volume is low. An off-line μSPE and ultra-performance LC-ESI-MS/MS (UPLC-ESI-MS/MS) method was developed and validated to determine procyanidins and anthocyanins in spiked plasma samples. The sample pre-treatment μSPE allowed the simultaneous determination of procyanidins and anthocyanins from plasma by using a small sample volume (350 μL) and without an evaporation step previous to the chromatographic analysis. Moreover, the use of UPLC technique allowed to determine the studied compounds at low concentration levels in a short analysis time (12.5 min approximately). Then, the developed method was applied to determine the studied compounds, procyanidins and anthocyanins, and their metabolites in rat plasma samples. Previously, the rats had consumed 5000 mg/kg of a grape pomace extract and the plasma was extracted 4 h after administration. The procyanidins catechin and epicatechin glucuronide, methyl catechin and epicatechin glucuronide, and methyl catechin and epicatechin sulphate were detected at μM concentration level, and the parent anthocyanins at nM.