This study was designed to investigate the nature of activities in an immersion English class and a non-immersion English class in the mainland of China, and to find out the differences between these two types of class through data gained from observation and interviews. Spoken discourse analysis was used to analyze the data, where Engestrom's activity complex system was used as the analytical framework to examine the nature of activities in the two types of classes. The results showed that it is the dynamic and situated nature of activity that makes a difference between the activities in these two classes. The interaction among the activity components, the social relations emerging through the process, the use of target language as the main mediational tool, and the subject content revealed in the activities enhance our emic understanding of the nature of activities. Implications can be drawn for English language teaching and for students' English language learning for the schools in the mainland of China. This study contributes to both immersion education and classroom interaction.