Objectives Chemoresistance is one of the major obstacles for gastric cancer (GC) treatment. Exosome-mediated transfer of circular RNAs (circRNAs) is associated with the drug-resistance in GC. Circ_0032821 has been reported as an oncogene in GC. This study is designed to explore the function and mechanism of Exosomal circ_0032821 in oxaliplatin (OXA) resistance of GC. Results Circ_0032821 was highly expressed in OXA-resistant GC cells, and exosomes secreted by OXA-resistant GC cells. Moreover, circ_0032821-containing exosomes secreted by OXA-resistant GC cells could boost OXA resistance, proliferation, migration, and invasion in OXA-sensitive GC cells. The mechanical analysis discovered that circ_0032821 acted as a sponge of miR-515-5p to regulate SOX9 expression. Circ_0032821 silencing and OXA treatment repressed tumor growth in the GC mice model. Conclusions Exosomal circ_0032821 boosted OXA resistance of GC cells partly by the miR-515-5p/SOX9 axis, hinting a promising therapeutic target for GC treatment.