The purpose of this study is to investigate the short-term and long-term effects of two kinds of advance organizers (AOs), a visual concept map and a text outline. The AOs were administered in a fully Web-based course in health care ethics. The outcome measures are students’ knowledge acquisition and application in two posttests. This study was conducted through a post-test only control group design with a random assignment. The population of the study involved 166 college students who participated in this online class in their junior or senior year. The voluntary research participants were randomly assigned into the two treatment groups and one control group. The treatment of AO was administered as an integral part of a one-week-long online module on the topic of patient-physician relationships. Students of the two treatment groups were presented with one of the two AOs, while the control group was instructed to proceed to textbook reading without an AO. Then, students were tested on the subject matter with two parallel posttests. Both posttests were composed of a multiple-choice question quiz and a set of scenario-based essay questions. The students took posttest I at the end of the instructional week, and posttest II four weeks after. A survey and interviews were also conducted to supplement the quantitative results with contextual information. The findings do not demonstrate a statistically significant AO effect among the treatment groups and the control group. However, in agreement with the previous research, this study shows a positive but inconclusive benefit of using AOs for students’ short-term knowledge acquisition. The students using a concept map consistently obtained higher learning achievements than individuals using a text outline. More importantly, this study reiterated the proposition that students of lower-learning abilities benefit more from using an AO for online learning than those of higher-learning abilities. The current study extends our knowledge on the use of AOs in fully Web-based educational environments. The results indicated that although AOs more often than not have small facilitative effects for learners, they are not equally effective for all learners in all learning situations. The incorporation of the instructional strategies, such as AOs, in Web-based courses and programs might benefit online learners, especially those students of lower verbal and analytical abilities, or of lower prior knowledge of the material-to-be-learned.