Objective To investigate the effects of ultrasound microbubble (UM)-mediated microRNA-545-3p (miR-545-3p) on the proliferation, migration, and invasion of thyroid cancer (TC) cells by regulating the E2F transcription factor 3 (E2F3) signaling pathway. Methods mRNA levels of miR-545-3p and E2F3 were detected in PTC cell lines (TPC-1, K1, TTA1) and TC tissues by quantitative reverse transcription-polymerase chain reaction. The relationship between miR-545-3p and E2F3 was detected by dual luciferase assay. Microbubbles were prepared using ultrasound technology, and TPC-1 cells were assigned to control, miR-negative control (NC), miR-545-3pmimics, UM+miR-545-3p-mimics, UM+miR-545-3p-mimics+pcDNA, and UM+miR-545-3p-mimics+E2F3 groups.The effects of ultrasound microbubble-mediated miR-545-3p on the proliferation, migration, invasion, and epithelialmesenchymal transition (EMT) of PTC cells by targeting E2F3 were detected. Expression levels of relevant proteins were detected by immunoblotting. Tumor transplant experiments were used to detect the effects of miR-545-3p on tumor growth and E2F3 expression. Results Expression levels of E2F3 mRNA were increased in TC tissues and TPC-1 cells, while expression levels of miR-545-3p decreased (P<0. 05). Online prediction of the Starbase database found that there was a targeted binding site between miR-545-3p and E2F3. The number of cell clones, scratchhealing rate, and number of invasive cells were lower in the miR-545-3p-mimics group compared with the miR-NC group, expression levels of E2F3, cyclin-dependent kinase (CDK) 1, matrix metalloproteinase (MMP)-2, MMP-9,N-Cadherin, and Vimentin were lower, while expression levels of miR-545-3p and E-Cadherin were higher ( P<0. 05). The number of cell clones, scratch-healing rate, and number of invasive cells were lower in the UM+miR-545-3p-mimics group compared with the miR-545-3p-mimics group, expression levels of E2F3, CDK1, MMP-2,MMP-9, N-Cadherin, and Vimentin were lower, while expression levels of miR-545-3p and E-Cadherin were higher(P<0. 05). Compared with the UM+miR-545-3p-mimics+pcDNA group, the number of cell clones, scratch-healing rate, and number of invasive cells were higher in the UM+miR-545-3p-mimics+E2F3 group, expression levels of E2F3, CDK1, MMP-2, MMP-9, N-Cadherin, and Vimentin were higher, and expression levels of miR-545-3p and E-Cadherin were lower (P<0. 05). Tumor volume and mass were smaller in the miR-545-3p-mimics group compared with the miR-NC group, while E2F3 expression levels were lower and miR-545-3p levels were higher (P<0. 05).Tumor volume and mass were smaller in the UM+miR-545-3p-mimics group compared with the miR-545-3p-mimics group, E2F3 expression levels were lower and miR-545-3p levels were higher ( P<0. 05). Conclusions UMmediated miR-545-3p inhibits the proliferation, migration, invasion, and EMT of PTC cells by targeting the E2F3 signaling pathway.