Objectives The purpose of this study was to investigate a teacher's experiences with integrated physical education(PE) lessons for different grades at a small-sized elementary school in autoethnography and the teacher’s educational meanings. Methods For this purpose, data was collected from the memory retrieval, in-depth interviews, and concerned documents of seven third graders, eight fourth graders, the investigator that was in charge in a third grade class and gave integrated PE lessons for different grades, and Kim Sae-ssak in charge of a fourth grade class at Tamheom Elementary School in Miji-gun, C Province during a semester from September, 2020 to January, 2021 to examine the teacher's experiences with integrated PE lessons for different grades and the teacher's educational meanings. Collected data was analyzed in a comprehensive analysis procedure based on practical eclecticism, and research integrity was secured through multi-sided analysis, inter-member review, and peer consultation. Results The teacher's experiences with integrated PE lessons for different grades were compared to a captain's story exploring an unknown territory. The teacher's experiences were categorized into “preparing for a voyage without a chart,” “striking on a rock upon departure,” “setting up a sail with steering adjusted” and “entering a cruise route.” The educational meanings of the teacher's experiences with integrated PE lessons for different grades were compared to a treasure hunt in a ship's log. The educational meanings were categorized into “expansion of lessons: expanded waters through marine explorations” in that the scope of lessons was expanded, “students' changes: changes to the sailors through an unknown voyage” in that changes were brought to students, and “a teacher's growth: the captain's growth amid waves” in that teacher made growth. Conclusions Since different grade-integrated PE lessons in small elementary schools have great educational significance for teachers, students, and the class itself, individual efforts and policy support are important.