The etiology of preeclampsia (PE) is complex and is known to involve the expression of circular RNAs (circRNAs). Among these, the function of circ_0090100 in PE is yet to be fully understood. This study was conducted to examine the expression profile of circ_0090100 in placental tissues from PE patients and to assess its influence on trophoblast cell functions. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to measure the RNA expression levels of circ_0090100, microRNA-139-5p (miR-139-5p), and AHNAK nucleoprotein (AHNAK). Cell viability, proliferation, apoptosis, and invasion were assessed using the CCK-8 assay, EdU incorporation, flow cytometry, and transwell migration assays, respectively. Western blot analysis was performed to detect the protein expression of N-cadherin, Vimentin, and AHNAK. Dualluciferase reporter assay and RNA immunoprecipitation (RIP) assay were conducted to elucidate the relationships between circ_0090100, miR-139-5p, and AHNAK. We found that the expression of circ_0090100 and AHNAK was upregulated, while miR-139-5p. expression was downregulated in PE placental tissues compared to controls. Transfection of a plasmid overexpressing circ_0090100 into JEG-3 and HTR-8/SVneo trophoblast cell lines resulted in reduced cell proliferation and invasion, but increased apoptosis. Mechanistically, circ_0090100 functioned as a miR-139-5p sponge, and miR-139-5p targeted AHNAK. Furthermore, upregulating miR-139-5p reversed the effects of circ_0090100 in JEG-3 and HTR-8/SVneo cells. AHNAK was found to be involved in the regulation of miR-139-5p effects on trophoblast cells. Additionally, circ_0090100 induced the production of AHNAK through miR-139-5p. Therefore, circ_0090100 activated AHNAK to suppress trophoblast cell proliferation and invasion, and promote cell apoptosis, via miR-139-5p.