Regarding the whispered use of technology in instruction and assessment of language skills, the present study investigates the effect of e-portfolio assessment on EFL learners' speaking proficiency. To this end, 60 intermediate students were randomly selected and homogenized to participate in the study. Samples of the IELTS speaking tests were then administered as the criterion for assessing the learners' speaking ability in the pre- and post-test over a ten-week period. In both groups (control and experimental), the students had discussions on the given topics and the instructor evaluated their performance. Only in the experimental group, however, the students tracked their progress by keeping e-portfolios. The performances of the learners in both groups were rated based on the IELTS speaking band descriptors; paired samples and independent samples t-tests were run to determine the impact of the treatment. In addition, the learners responded to an attitude questionnaire and attended an interview to express their attitudes toward using e-portfolios in their speaking classes. The findings showed that not only using e-portfolio assessment improved the learners' overall speaking proficiency significantly but it also improved the students' positive attitudes toward its use as a learning and assessment tool. Moreover, the potential bias of the functionality of e-portfolios and the dependability of the findings were checked through running differential item (DIF) functioning and generalizability analyses, both suggesting the utility of the findings.