Recent evidence revealed that circular RNAs (circRNAs) are key regulators for tumorigenesis. However, their roles in papillary thyroid cancer (PTC) is not fully understood. In the current work, the differentially expressed circRNAs between PTC tissues and adjacent noncancerous tissue samples were screened by circRNA microarray. We further selected the highest expressed circRNA (circ_0025033) in tumorous tissues for the study. qRT-PCR was used to measure the level of circ_0025033 in PTC tissue samples and cell lines. Gain/loss of function assays were carried out to determine the effect of circ_0025033 on cell viability, clone-forming, apoptosis, migration and invasion. Dual-luciferase reporter assays were conducted to investigate the mechanisms of circ_0025033 in PTC. The data showed that circ_0025033 aggravated cell proliferation, migration and invasion and inhibited cell apoptosis. Additionally, circ_0025033 could directly sponge miR-1231 and miR-1304 in PTC cells. Furthermore, the oncogenic role of circ_0025033 is dependent on its suppression of miR-1231 and miR-1304. Collectively, this work uncovers a novel signal of circ_0025033/miR-1231/miR-1304 involved in PTC initiation and progression. (C) 2019 Elsevier Inc. All rights reserved.