ABSTRACT Vocabulary is central to language and words are of critical importance to the typical language learners. In this paper, I will report on research findings of an investigation, which was carried out at the University of Macau between 2001 and 2003, on how students from a high school in Macao were helped to build and enlarge their vocabulary size by analyzing the effectiveness of two modes of teaching, teacher instruction and computer input. One hundred and eight students volunteered to take part in this research project. These students were divided into two groups with equal numbers, 54 in each. Students in group A were required to learn in a computer lab, each having a computer in front of him or her and those in Group B were placed in a classroom with no access to the computer (i.e., a traditional classroom). Three vocabulary tests were administered respectively to them over a period of 6 weeks. A survey was conduced after these tests to elicit opinions about how they felt while taking the tests and about whether they were satisfied with their test performance. Test results and survey findings, which were analyzed descriptively and inferentially, show that students who had an opportunity to "play" with pictures that appeared on the computer screen seemed to be more ethusiastic and motivated than those without such an opportunity. Data does not, however, show a significant difference between the two groups om vocabulary acquisition. This means that there is no clear evidence to support the finding could be useful for achieving a better understanding of the value in teaching vocabulary of computer-assisted learning and teacher instruction in vocabulary development.