Abstract: 【Objective】 This study aimed to investigate effects of combined exposure to 17α-methyltestosterone （MT） and polystyrene microplastics （PS-MPs） on ovarian transcriptomes of zebrafish， to provide a theoretical basis for scientifically assessing potential risks of combined pollution to fish reproductive health.【Method】 The experiment set up the control group （0.001% absolute ethanol exposure）， MT group （50 ng/L MT exposure）， the MT+PS-MPs group （50 ng/L MT combined with 0.5 mg/L PS-MPs exposure）. The ovarian tissue was dissected and the ovarian tissue structure of zebrafish was observed by hematoxylin and eosin staining. The relative expressions of key genes for steroid hormone synthesis in zebrafish were detected by real-time fluorescence quantitative PCR. Transcriptome sequencing analysis was performed on samples of control and MT+PS-MPs groups. The reliability of transcriptome sequencing data was verified by real-time fluorescence quantitative PCR.【Result】 Compared with control group， the ovaries of zebrafish in MT group showed obvious vacuolization， and the proportion of mature egg cells decreased significantly. The relative expressions of cyp11a1 and cyp19a1a genes were significantly decreased （P<0.05， the same below）， and the relative expressions of StAR and cyp17a1 genes were extremely significantly decreased （P<0.01， the same below）. Compared with MT group， the ovarian structure of zebrafish in MT+PS-MPs group was more severely damaged； the ovarian tissue was occupied by a large number of primary oocytes， and almost no mature egg cell could be observed. Compared with control group， the relative expressions of StAR， cyp11a1， cyp17a1， and cyp19a1a genes in MT+PS-MPs group were extremely significantly decreased. DEGs screening results showed that 421 DEGs were identified in the ovarian tissues of zebrafish in control and MT+PS-MPs groups， among which 156 DEGs were significantly up-regulated and 265 DEGs were significantly down-regulated. The GO functional annotation results showed that 393 DEGs were annotated into three major categories： biological processes， cellular components， and molecular functions. The KEGG signaling pathway enrichment analysis results showed that among the top 20 enriched signaling pathways， seven significantly enriched signaling pathways were related to growth and development including regulation of actin cytoskeleton， cell cycle， cell adhesion molecules， apoptosis adherens junction，Wnt signaling pathway， and mTOR signaling pathway； four significantly enriched signaling pathways were closely related to metabolic processes， including lysine degradation， one carbon pool by folate， glutathione metabolism， as well as alanine， aspartate， and glutamate metabolism.【Conclusion】 PS-MPs can intensify the toxic effects of MT on ovaries of zebrafish. The mechanism involves the synergistic inhibition of expression of key genes for steroid hormone synthesis， and may affect physiological functions of the ovaries by interfering with the key signaling pathways that regulate cell growth， development， and metabolism， ultimately leading to the obstruction of follicular development.