The main purpose of this paper is to explore and discuss the main characteristics of project-based online learning (PBOL) to promote learners' critical learning skills through reusable learning objects (RLOs) from global online resources. Based on the main purpose of this study and the concerns, the key research inquiries are: (1) How does a PBOL environment improve the learners' critical thinking skills via RLOs? (2) What are the patterns of the learners' critical thinking skills in a PBOL environment when they focus on building and delivering RLOs? and (3) What are the learning impacts and communicational outcomes of a PBOL environment on the learners' critical thinking skills when they work with RLOs? This is a qualitative case study that utilizes both qualitative and quantitative data to provide detailed information to the researcher for the data collection. The research site was the Designing and Delivering an E-Learning Environment graduate course at the Department of Distance Education of Social Sciences Institute in the large urban and government-based University in the Spring Semester 2004. There were totally I I learners (three of them were men and the rest of them were women) in this course. (C) 2006 Elsevier Ltd. All rights reserved.