Problem-solving skills are part of Critical Thinking which focuses on the student's abilities to face the 21st century. Recently, one technique to foster and improve problem-solving skills is by learning through Computational Thinking. Many previous studies have described that Computational Thinking is a problem-solving technique adopted from Computer Sciences. However, Computational Thinking learning had been carried out in class or asynchronous. The COVID-19 situation raises the challenges of how Computational Thinking can be taught online. Therefore, this study aims to develop an instructional design in online-based computational thinking learning. The development of this study employs the ADDIE method. The final step of the development stage was carried out through a small-scale online class experiment. The development result obtained by Scratch, which is an online programming platform that is suitable for 1) learning Computational Thinking, 2) instructional design that refers to problem-based learning, and 3) instructional strategies that refer to Bloom's taxonomy. The results of the small-scale instructional design experiment showed that there was a significant improvement in the students' ability in problem-solving and computational thinking.