An interlaboratory study was conducted in 11 laboratories to validate an ELISA method developed for the quantitative determination of egg white proteins (EWPs) in foods. The ELISA kit used for this study is based on sheep polyclonal antibody. It does not produce any false-positive results or cross-reactivity in a broad food matrix range with zero EWP content. All participants obtained the Egg ELISA Kit-native with standard operational procedure and the list of samples, as well as the samples and a protocol for recording test results. The study included 10 food samples. Four samples of food matrix with zero EWP content showed EWP content lower than the first standard (EWP content 0.5 mg/kg). One sample of food matrix with zero EWP content revealed EWP content higher than standard 3 (1.5 mg EWP/kg). Five food samples containing EWP as an ingredient tested positive and one negative. The statistical tests (Cochran, Dixon, and Mandel) and analysis of variance were used to evaluate the interlaboratory study results. Repeatability and reproducibility limits, as well as LOQ (1.4 mg EWP/kg) and LOD (0.43 mg EWP/kg), were calculated for the kit.