Abstract: To find out the main sources of measurement uncertainty in the data of carbamate pesticides determination in vegetables by NY/T761\|2008， methomyl residues in cowpea were determined by liquid chromotography(LC). The sources of uncertainty in the whole measuring process were analyzed， and the uncertainty components were evaluated. Ultimately， the relative synthesis standard uncertainty and the relative expansion uncertainty were calculated out. It was showed that measurement uncertainty was mainly derived from the two procedures of peak area of sample solution and solution volume. Therefore， it was necessary to confirm the good state of LC instrument and precise operation in two forementioned procedures for decreasing measurement uncertainty．

Key words: uncertainty, methomyl residue, carbamate pesticides, LC