Ovarian cancer is characterized by transcoelomic metastasis into the peritoneal cavity. The peritoneal malignant ascites is enriched with ovarian cancer cells and a small amount of tumor-associated immune cells which create a unique microenvironment actively contributing to progression of the disease. However, it remains unclear how cancer cells communicate to its local environment under the influence of chemotherapy. To address this issue, we performed LC-MS/MS analyses of several primary cultures of ovarian cancer cells from chemonaive malignant ascites incubated for 3 days with autologous pre- or post-chemotherapy ascitic fluids. Enrichment analysis identified prominent upregulation of proteins associated with pathways of DNA repair and cell cycle regulation in tumor cells incubated with ascitic fluids after chemotherapy. Consistently with these data, ascites after therapy increased the resistance of ovarian cancer cells to cisplatin. These findings demonstrate that under stress condition cancer cells can secrete signaling molecules into the extracellular space and contribute to the emergence of tumor chemoresistance during short time period.