The growing use of game-based simulation in healthcare education reflects the opportunities afforded to learners by serious games, which simulate real-world situations and enable students to emulate the roles of healthcare professionals in a safe and engaging learning environment. As part of a design-based research project to design, test, and evaluate an online 3D simulation game for use in game-based simulation in healthcare education, the present study applied Kolb's experiential learning theory to investigate nursing students' experiential learning processes during a 3D simulation game. The data, collected from eight nursing students, comprised audio and video recordings from gaming sessions and focus group interviews. The results indicate that in 3D simulation game, patient-related experiences were supported by audiovisual authenticity, the authenticity of scenarios, and interactivity. Feedback triggered students to reflect on their own learning processes. Students conceptualised knowledge by applying nursing theory, and they internalised procedures that can be used in real life. They also had an opportunity to experiment by exploring and making decisions in the gaming environment. One of the main issues arising from these findings is that 3D simulation games used in game-based simulation should share familiar characteristics of leisure games to ensure an engaging learning experience.