This article reports the results of an experimental study on the effectiveness of mobile technology (WhatsApp) in improving the critique writing skills of English as a Foreign Language learners and increasing their motivation for learning. The participants (n = 52) are Average-English proficient learners enrolled in two writing courses given at two English-medium universities. The study employed the factorial mixed methods pretest-posttest control group experimental design whereby two intact Sophomore Rhetoric classes were randomly assigned to control and experimental conditions. The experimental conditions included the integration of the WhatsApp application into the experimental group class, whereas participants in the control group were given the regular Sophomore Rhetoric instruction with no WhatsApp mediation. Descriptive statistics (means and standard deviations) and two Analysis of Covariance (ANCOVA) tests were used to address the questions raised in the study. Qualitative data using 2 questionnaires including open-ended question and quantitative data using Pretests and posttests were collected. Results indicated that the use of the WhatsApp mediation was more effective than the regular instruction in improving the critique writing proficiency of the participants and in increasing their motivation for learning.