High mortality from high-grade serous ovarian cancer (HGSOC) is caused by its late detection due to the absence of early symptoms and lack of tests for early detection. Therefore, it is necessary to better understand molecular mechanisms of its development, which could create new diagnostic and therapeutic approaches. The goals of my research were: to determine by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), on an extended set of HGSOC and healthy fallopian tube samples, expressions of apoptosis regulator gene BCL2, its transcription factors GLI1 and GLI2, two microRNAs (miRNAs) that can target BCL2, miR-96-5p and miR-21-5p, and two long non-coding RNAs (lncRNAs) that can also bind these miRNAs, MALAT1 and XIST; based on the correlations between determined expressions, to construct a network of mRNAs–miRNAs–lncRNAs that could explain epigenetic regulation of BCL2 by non-coding RNAs, and to determine diagnostic value of these expressions for discrimination between tumor and healthy tissue. Results showed that expressions of BCL2, GLI1, and both lncRNAs were significantly decreased, while expressions of both miRNAs were increased in ovarian cancer. Correlation analysis showed that transcription factor GLI1 could play more important role than GLI2 in BCL2 expression regulating, and that BCL2–miR-96-5p–XIST axis could be the cause for decreased BCL2 expression in HGSOC. Expressions of BCL2 and XIST showed highest diagnostic values (AUC> 0.8).