Purpose: Papillary thyroid carcinoma (PTC) is the most prevalent endocrine malignancy, and the global incidence has been steadily increasing over the years. Although PTC generally exhibits favorable prognosis, a subset of patients experiences aggressive progression and increased mortality. Current prognostic approaches, reliant on clinic-pathological factors, have limitations, underscoring the need for innovative biomarkers. MicroRNAs (miRs) have emerged as promising candidates due to their roles in cellular processes and cancer progression. Among them, the present study investigated the role of miR-18b in PTC, exploring its potential as a prognostic biomarker. Methods: Utilizing PTC cell lines (TPC1, K1), we examined miR-18b expression and its regulatory effects. The present study used web-based tools to predict the target of miR-18b and to investigate the prognostic impact of miR-18b on thyroid cancer. Results: Through a series of cell proliferation, invasion assay, gap closure, and colony formation assays, we identified that miR-18b suppresses PTC aggressiveness. Dual-luciferase assays confirmed that miR-18b directly targeted the 3’-untranslated region of CDK2 and suppressed the expression of CDK2. In addition, miR-18b significantly attenuates the interaction between cyclin A or cyclin E with cyclin-dependent kinase 2 according to co-immunoprecipitation assay.Western blotting of cell cycle proteins and flow cytometry revealed miR-18b–induced cell cycle arrest and apoptosis. Conclusion Our findings underscore miR-18b’s potential as a biomarker for predicting the prognosis of PTC and suggest that it functions through direct regulation of CDK2, influencing cell cycle dynamics. This study not only enhances our understanding of miR-18b in thyroid cancer but also highlights its potential in refining prognostic evaluations and therapeutic strategies.