The study investigated the effects of explicit vocabulary instruction on students’ vocabulary retention, and on their reading comprehension in 11th grade at Shinta Preparatory School, Gondar. The study was a quasi-experimental in design. Out of the five sections, two sections (11th C= and 11th E=: a total of 93 students) were randomly selected. Explicit instruction was used for the experimental group whereas conventional methods were used for the control group. In addition, vocabulary retention and reading comprehension tests were used to collect data. Accordingly, the results of the independent sample t-test showed that there was a statistically significant difference between the experimental, and the control groups in their vocabulary retention (P < 0.05, i.e., p = 0.003), and in their reading comprehension (p < 0.05, i.e., p = 0.000) respectively. Similarly, a paired sample t-test was used to compare post-test, and delayed post-test results. The result of the comparison showed that the experimental group retained more vocabulary than the control group since the mean difference between the tests was close to zero (i.e., 0.120) and p > 0.05. Finally, the overall test results indicated that explicit instruction improved students’ vocabulary retention and reading comprehension than conventional methods. Thus, the findings from this study pointed out that explicit vocabulary instruction was one of the most effective methods for improving students’ vocabulary retention and reading comprehension.