Nanoparticles are used as a new group of elicitors for the production of valuable metabolites. In the present study, the effects of silicon dioxide nanoparticles (SiO2 NPs) as abiotic elicitor on some phytochemical traits in H. reticulatus and H. pusillus hairy root cultures were analyzed. Hairy roots were obtained from cotyledon (H. reticulatus) and leaf (H. pusillus) explants Inoculated with Agrobacterium rhizogenes. The effect of silicon dioxide nanoparticles concentrations (0, 25, 50, 100 and 200 mg L-1) with two exposure times (24 and 48h) on fresh weight, antioxidant capacity and some polyphenol compounds in hairy roots of two Hyoscyamus species were investigated. Results showed that the highest hairy roots fresh weight (10.48 g) were found in the medium treated with 25 mg L-1 SiO2 NPs at 48 hours of exposure time in H. pusillus hairy root cultures. Overall High amount of DPPH (18.05%) and FRAP (6.26 mmol Fe+2 g-1 FW) was observed in H. reticulatus hairy roots elicited by 25 and 200 mg L-1 SiO2 NPs at 48 and 24h of exposure time, respectively. Rosmarinic acid content (9.02 μg g-1 FW) with 1.65-fold boost compared to control, was observed in H. reticulatus hairy roots culture elicited with SiO2 NPs (25 mg L-1) after 48 h exposure time, while this compound was not detected in H. pusillus hairy roots. The results demonstrate that silicon dioxide nanoparticles can be used as effective and abiotic elicitor to increase some polyphenol compound and antioxidant capacity in H. reticulatus and H. pusillus hairy root cultures.