Background: Nanoparticles (NPs) are small-sized particles with dimensions of 1 - 100 nm that have various medical and pharma-ceutical technology applications. Objectives: In this study, we aimed to develop a quick, green, and eco-friendly procedure for the synthesis of gold NPs (AMGNPs) using the aqueous extract of Achillea millefolium (AM) and evaluate the e ects of them on preantral follicle (PF) maturation in vitro compared to commercially provided GNPs (C-GNPs) and the AM extract alone. Methods: We assessed PF maturation through the morphological assessment of follicles, diameter changes, and estradiol and pro-gesterone levels in PF. We also evaluated the morphometric indices in the control group and groups treated with the AM extract, green GNPs, and C-GNPs. Results: The results showed that the AM extract had positive e ects on the PF development by increasing the production of estradiol. The evaluation of PF treated with C-GNPs one to four days after the treatment showed that the mean diameter of follicles was sig-nificantly reduced in the C-GNPs group compared to the control group. Moreover, the mean estradiol level increased, and the mean progesterone level decreased in all the experimental (10, 25, 50, and 100 µg/mL of C-GNPs, green GNPs, and the AM extract) groups compared to the control group (P-value < 0.05). The size and concentration of the NPs were 20 nm and 150 µg/mL, respectively. Conclusions: The findings suggest that green GNPs synthesized with the AM extract can minimize the hazardous e ects of NPs and have beneficial e ects on the development and growth of PF.

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