The method performance and matrix effect related to quantitative determination of pesticide residues was assessed after QuEChERS extraction and LC-MS-MS analysis. Dicloran, phosmet and phosmet-oxon, pirimiphos-methyl, and BNOA were analyzed in peach, apple, melon, cereals, tomato, and strawberry. The matrix effects, as well as recovery and process efficiencies, were determined for a fungicide, two insecticides, and a plant growth regulator. Crop samples were spiked either pre- or post-extraction, then the peak area was compared with the peak area in neat solvent. The mean recovery ranged from 73% to 98%, and repeatability (as RSD) was between 3% and 16%, depending on the compound and spiking level. The matrix effect occurred as ionic suppression and was found in the range of 5% to 22% depending on the compound. Recovery efficiencies were good and substantially comparable, being in the range of 93-96%. Although the suppression observed still appears to be acceptable considering the overall process efficiency, it seems evident that the matrix effect is important when a reliable quantitative method must be applied.