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Exosomes derived from mesenchymal stem cells (MSC-exo) have the potential to regulate cancer progression by delivering various molecules, including long noncoding RNAs (lncRNAs). This study aimed to investigate the functional role and underlying mechanism of exosomal LINC00900, derived from human adipose-derived mesenchymal stem cells (MSCs), in thyroid cancer (TC). MSC-exo was isolated from conditioned medium using differential ultracentrifugation, observed under transmission electron microscopy, and identified through western blotting and an uptake assay. Cell viability, apoptosis, cell cycle progression, and invasion were evaluated by cell counting kit-8 (CCK-8) assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, flow cytometry, and transwell invasion assay, respectively. RNA-pull down and RNA immunoprecipitation assays were conducted to evaluate the interaction between LINC00900 and polypyrimidine tract binding protein 1 (PTBP1). A mouse model with subcutaneous xenografts of the TC cell line TPC-1 was used to assess tumor growth in vivo. The isolated MSC-exo exhibited classic exosome characteristics and could effectively be delivered to TPC-1 cells. MSC-exo significantly inhibited the proliferation of TPC-1 cells and promoted their apoptosis, as evidenced by a decreased optical density value and an increased percentage of apoptotic cells. Following incubation with MSC-exo, LINC00900 expression was markedly increased in TPC-1 cells. Overexpression of LINC00900 or inhibition of PTBP1 suppressed cell proliferation, elevated G0/G1 ratio, and promoted cell apoptosis. Additionally, LINC00900 expression was reduced, while PTBP1 protein levels were increased, in cancer tissues from TC patients. Furthermore, PTBP1 was identified as a target of LINC00900 and was negatively regulated by it. LINC00900 was also confirmed to inhibit cell autophagy by downregulating PTBP1. In vivo, MSC-exo inhibited tumor growth and autophagy while promoting apoptosis in TPC-1 cell xenografts. In conclusion, MSC-Exo carrying LINC00900 can effectively inhibit tumor cell growth in TC via suppression of PTBP1.