The objective of this study was to investigate the effects of three different screen sizes (small, medium and large) and two types of multimedia instruction (text only and text with pictorial annotation) on vocabulary learning. One hundred thirty-five Korean middle school students learning English as a foreign language were randomly distributed into six groups and were given a pretest, a self-study multimedia instruction, a posttest and a retention test online. The pretest, posttest and retention test were identical and included 30 vocabulary questions. Results show that the large screen multimedia instruction helped the students to learn English vocabulary more effectively than the small screen instruction as demonstrated on both the posttest and retention test. However, there was little difference in vocabulary learning between the text-only and text-with-pictorial annotation instructions. Although visual perception can be influenced by each learner's expectations and knowledge, using a smaller screen for instruction causes more challenges for learners to perceive and comprehend vocabulary learning.