This study presents the first records of the Broad-tail Stingray, Bathytoshia brevicaudata (Hutton, 1875), in the East China Sea, significantly extending its known distribution in the Northwest Pacific. Through comprehensive morphological examination of male and female specimens, we identified several sexually dimorphic traits, including the number of oral papillae rows, dorsal tubercle spines, and tooth cusp morphology. Stomach content analysis revealed predation on teleosts exceeding 30 cm total length, challenging previous dietary descriptions. Furthermore, the co-occurrence of distinct fishing hook types (coastal J-hook and pelagic circle hook) within one specimen provides empirical evidence of transboundary movements between neritic and oceanic zones. We also sequenced and characterized the complete mitogenomes of both sexes (17,640 bp; GenBank: PV699610–PV699611), which exhibited conserved dasyatid genomic features, including pronounced AT bias (59.2%), purifying selection across protein-coding genes (strongest in cox2), and structural traits such as an incomplete stop codon in ND4 and a DHU-arm-deficient trnS1. These integrative findings enhance the ecological and molecular understanding of B. brevicaudata and provide critical baseline data for its conservation in poorly studied regions of the Indo-Pacific.