<![CDATA[Mathematics is closely related to various aspects of human life, including culture. One approach that integrates mathematics with culture is ethnomathematics, which enables mathematics learning to become more contextual and meaningful. However, previous ethnomathematics studies have primarily focused on cultural objects such as batik, traditional houses, traditional games, and handicrafts, while studies examining carnival costumes remain limited. This study aims to explore the ethnomathematical concepts embedded in the costumes of the Pesona Gondanglegi Carnival, namely the Raja Garuda Costume, Mahkota Diablo Costume, and Javanese Costume, and to describe their potential as contextual resources for mathematics learning. This study employed a qualitative approach with an ethnographic design. Data were collected through observations, semi-structured interviews with the owner of MIZU PROJECT, and documentation. Data were analysed using the interactive model of Miles, Huberman, and Saldaña, which consists of data condensation, data display, and conclusion drawing. The trustworthiness of the findings was ensured through technique triangulation and source triangulation. The findings revealed that the three carnival costumes embody various ethnomathematical concepts, including reflection, arithmetic sequences, and geometric sequences, as represented in the arrangement of ornaments, shapes, and decorative patterns. These concepts can be mathematically modelled and integrated into mathematics learning, particularly in the topics of geometric transformations and number sequences. Therefore, the costumes of the Pesona Gondanglegi Carnival have the potential to serve as contextual learning resources that integrate local cultural values with mathematical concepts, thereby supporting meaningful mathematics learning while contributing to the preservation of local culture. Keywords: ethnomathematics, Pesona Gondanglegi Carnival, carnival costumes, number sequences, reflection.]]>
