Objective. To assess the level of DNA damage and gene expression of  HAS2, COX2 and GREM1 in cumulus cells in mice with experimental thyroiditis. Material and methods. Experimental thyroiditis in mice was induced by daily administration of merkazolil (50 mg/kg). Cumulus-oocyte cellular complexes (COCs) were extracted from murine ovarian follicles. Immediately following COCs retrieval, the cumulus was stripped from the oocyte. DNA damage in cumulus cells was detected by DNA comet assay; and cumulus gene expression for COX2, HAS2 and GREM1 at mRNA level was assessed using reverse transcription polymerase chain reaction. Results. The results showed that experimental thyroiditis causes the death of 17% of cumulus cells. The number of cells with damaged DNA was 46.2%. The GREM1 mRNA levels decreased in 1.65 times (р<0,05), the expression of COX2 and HAS2 did not changed. Conclusion. The genome integrity of cumulus cells surrounding the oocyte is disrupted due to experimental thyroiditis. The change in GREM1 gene expression can be indicator of ovarian disfunction.