This study aimed to improve students’ mathematics learning interest and collaboration skills in learning whole numbers through a relay game integrated with Problem-Based Learning (PBL). This classroom action research, based on the Kemmis and McTaggart model, was conducted in two cycles involving 27 students of Class IIIB at SD Negeri Tamanan Kota Kediri from August 11 to September 15, 2026. Each cycle consisted of three meetings; the first meeting of Cycle I involved group discussions using student worksheets, while the relay game was implemented in the following five meetings. Data on mathematics learning interest were collected using a 24-item questionnaire, while collaboration skills were assessed using an observation sheet covering three aspects, and the data were analyzed descriptively. The success criterion for learning interest was determined based on the mean interest score reaching the high category, with a score range of 72–96. Before the intervention, 16 students (59.3%) had low learning interest, none had high learning interest, and the mean collaboration score was 41.36. In Cycle I, no students had low learning interest, 20 students (74.1%) had moderate learning interest, and 7 students (25.9%) had high learning interest, with a mean collaboration score of 55.25 (fair). In Cycle II, 18 students (66.7%) had high learning interest and 9 students (33.3%) had moderate learning interest, with a mean collaboration score of 82.72 (good), indicating that the predetermined success criteria were achieved. The descriptive improvement occurred alongside several refinements to the intervention, including assigning relay turns based on students’ numbers or draws, providing appreciation to all groups, varying the learning media, and providing individual assistance. Because there was no comparison class and the learning materials differed across meetings, the improvement cannot be attributed solely to the relay game. The relay game integrated with PBL can serve as an alternative instructional approach for improving elementary school students’ learning interest and collaboration.