FSH may increase the risk of ovarian malignancy and play a key role in ovarian carcinogenesis, although the mechanism (s) are undefined. HMGA2 overexpression has been observed to be an early genetic event in tumorigenesis. The present study was designed to investigate the effect of FSH on let-7, HMGA2 and p53 expression in normal fimbrial epithelial cells of ovarian high-grade serous carcinomas (HGSCs). A primary human Fallopian tube (FT) fimbrial epithelium ex vivo culture system of low-grade serous carcinomas (LGSCs) and HGSCs was established. The levels of HMGA2, let-7, p53 and FSHR were evaluated by western blotting and reverse transcription (RT)-PCR. Treatment with FSH significantly increased HMGA2 expression in a time-dependent manner and the let-7 expression levels decreased gradually over time in the normal fimbrial epithelial cells of HGSCs. However, we did not observe similar results in LGSCs. In addition, knockdown of let-7 suppressed HMGA2 expression. p53 was not detected in the normal fimbrial epithelial cells before or after FSH administration. Our results indicate that FSH increases the expression of HMGA2 by downregulating the expression of let-7 in normal fimbrial epithelial cells of HGSCs, but no occurrence of p53 mutation. The susceptibility of fimbria to FSH in HGSCs compared with those in LGSCs is different.