Second language studies have supported the use of glossing for enhancing vocabulary learning. Along with technological developments, an increasing number of studies have examined electronic textual glossing in computer-assisted environments, yet only a small number of studies have compared electronic glossing to its traditional paper counterpart. In the present study, we examined the effectiveness of electronic and paper textual glosses on second language vocabulary learning and reading comprehension within a cognitive load theory framework. We adopted an experimental design using Korean undergraduate learners of English as a foreign language, who read a target text under one of the three reading conditions: electronic gloss, paper gloss, and no gloss. The results showed that the electronic glossing condition resulted in the greatest gains of vocabulary. The electronic glossing condition was also the most efficient in light of the cognitive load framework, showing the highest instructional efficiency. However, there were no significant differences among the three reading conditions for measures related to reading comprehension.