Preeclampsia (PE) is a potentially fatal pregnancy complication; however, its pathogenesis remains unclear. Long non-coding RNAs (lncRNAs) are associated with occurrence and progression of PE. Therefore, this study aimed to explore the function of the lncRNA prospero homeobox 1-antisense RNA 1 (PROX1-AS1) and elucidate its underlying molecular mechanism of action. We found that the expression levels of PROX1-AS1 were elevated in both the placental tissues and blood samples of the patients with PE. Moreover, the results of the flow cytometry and transwell assay showed that the knockdown of PROX1-AS1 inhibited the apoptosis and promoted the migration and invasion of HTR-8/SVneo cells. We also assessed the interactions between PROX1-AS1, caspase-9, and microRNA (miR)-211-5p via dual-luciferase reporter and RNA pull-down analyses. The data indicated that PROX1-AS1 acted as a sponge for miR-211-5p to regulate the expression of caspase-9. Moreover, the expression of miR-211-5p was reduced in PE and negatively related to PROX1-AS1, while that of caspase-9 was increased in PE and negatively regulated by miR-211-5p. Furthermore, inhibition of miR-211-5p rescued the facilitation of cell apoptosis, migration and invasion induced by the knockdown of PROX1-AS1. We also found that caspase-9 improved the apoptosis rate, and suppressed the cell migration and invasion induced by the overexpression of miR-211-5p. In conclusion, the knockdown of PROX1-AS1 promoted the cell morbidity of the trophoblast cells by modulating the miR-211-5p/caspase-9 axis, which may alleviate the progression of PE. This novel regulatory network may contribute to the pathogenesis and progression of PE.