In order to investigate the physiological responses of black cumin seed (Nigella sativa L.) under different concentrations of silver nanoparticles (0, 2.5, 5, 10, 20, 40 and 80 mg/L AgNPs), a completely randomized design experiment was conducted with 5 replications in the greenhouse of Shahed University in 2018. In the present study, growth traits, photosynthetic pigments, anthocyanins, proline content, glycine betaine, soluble and insoluble sugars, phenolic compounds and gas exchange and fluorescence parameters of the photosynthetic apparatus were investigated. The results showed that the AgNPs treatments significantly inhibited biomass production and the growth of root and shoot, and decreased the contents of chlorophyll a and b at high concentrations (20, 40 and 80 mg/L), while the AgNPs treatments increased the content of carotenoids, proline, glycine betaine, soluble sugars, anthocyanins and phenolic compounds compared to control treatment. By increasing the concentration of AgNPs, photosynthetic rate, transpiration rate, stomatal conductance, the maximal quantum yield of PSII photochemistry, photochemical quenching coefficient and effective quantum yield of PSII photochemistry declined. Measurements of ﬂuorescence showed strong evidence of inhibitory effects on energy transfer from light harvesting complexes to reaction centers, the deterioration of the PSII water splitting system and the inactivation of PSII reaction centers at high concentrations of AgNPs. In conclusion, the results demonstrated that AgNPs induced an inhibitory mechanism on photosynthetic processes and biomass of black seed plants.