This study aimed to assess the impact of a lecture on knowledge about dementia prevention conducted by pharmacy students for visitors at dementia café. A pre- and post-intervention design was used to evaluate comprehension, effectiveness, and retention of knowledge. The lecture focused on the diet and sleep regime recommended for dementia prevention. First, before the lecture, the visitors were asked to complete a written test that contained three multiple choice and four open-ended questions. The pre-test also asked questions related to a poster on the subject, to which the visitors were exposed in the café. After the lecture, a post-test was conducted with the same content as the pre-test. The analysis revealed that the post-test scores were significantly higher than the pre-test scores. Furthermore, participants took a remade test with three multiple choice and three open-ended questions. This additional test related to the questions on which the participants received low scores in the pre-test. The evaluation of the remade test was conducted over a period of four months. During all four months of the evaluation, the scores for the remade test were found to be above 75. The validity of the lecture and of knowledge retention were proved through these tests. Based on these results, it can be concluded that the lectures contributed to an increase in the knowledge of dementia prevention among the visitors at the café.