With the dramatic increase in nanotechnologies, it has become probable that biological systems will be exposed to an excess of nanoparticles (NPs). Purslane (Portulaca oleracea L.) is an annual grassy plant that has some pharmacological properties such as antibacterial, analgesic, wound healing, skeletal muscle-relaxant, anti-inflammatory and a radical scavenger. In this study, the effect of different concentrations of silver nanoparticles (0, 2.5, 5, 10, 20, 40 and 80 mg/L) on the growth and biomass production, photosynthetic pigments, proline, flavonoid and phenolic compounds, gas exchange capacity and chlorophyll fluorescence parameters were investigated in purslane plants. The results showed that AgNPs treatments significantly inhibited biomass production and the growth of root and shoot, and decreased the content of chlorophylls a and b at high concentrations (20, 40 and 80 mg/L), while, the AgNPs treatments increased the content of carotenoids, 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. The measurements of Chl a ﬂuorescence showed that strong evidence of inhibitory effects on energy transfer from light-harvesting complexes to reaction centres, the deterioration of the PSII water splitting system and the inactivation of PSII reaction centres at high concentrations of AgNPs. In conclusion, our results demonstrated that AgNPs induced an inhibitory mechanism on photosynthetic processes and biomass of purslane plants.