Magnetic topological materials LnSbTe (Ln = lanthanide) have attracted intensive attention because of the presence of interplay between magnetism, topological, and electron correlations depending on the choices of magnetic Ln elements. Varying Sb and Te composition is an efficient approach to control structural, magnetic, and electronic properties. Here, we report on the composition-dependent properties in PrSbxTe2-x. We identified the tetragonal-to-orthorhombic structure transitions in this material system and very large negative magnetoresistance in the x=0.3 composition, which might be ascribed to the coupling between magnetism and transport. Such unusual magnetotransport enables PrSbxTe2-x topological materials as a promising platform for device applications. © 2025 American Physical Society.