Objectives Granulosa cells are associated with steroidogenesis and ovarian function in females. Aims of the study are to understand the effects of gold nanoparticles (AuNP) on steroidogenesis and apoptotic pathway associated genes in buffalo granulosa cells. Results The AuNP were prepared chemically and thereby characterized by transmission electron microscope (TEM) imaging, absorbance and dynamic light scattering (DLS) measurements for hydrodynamic diameter and zeta potential. The cultured buffalo granulosa cells (BGC) were co-incubated with AuNP in two concentrations (2 x 10(9) and 2 x 10(10) AuNP/ml) for 24 h. Treatment of BGC with AuNP significantly modulated the steroidogenesis associated genes (3 beta-Hsd and Cyp19A1) expression and progesterone accumulation in the culture fluid. AuNP affected the apoptotic pathway in BGC by affecting the gene expression of Caspase-3, Bad and Bax. The AuNP did not exert oxidative stress through anti-oxidant induction & lipid peroxidation in the buffalo GC. Conclusions AuNP may modulate the endocrine system by having impact on the steroidogenesis pathway and also have the potential to affect apoptotic pathway in a buffalo granulosa cell model.