Nanotechnologies are in continuous development with fields of inexhaustible application, such as the production of building materials and dyes, food technologies, pharmaceutical and cosmetics industry, environmental protection and medicine. In parallel with the development of nanomaterials manufacturing technologies and diversification of their use areas, researches on the issue of their toxicity and environmental impact become very current. However, some studies have revealed positive effects of these materials on cell growth or metabolic activity. Results of nanoparticles action on microalgae are very varied, and their effects will depend on nature and size of nanoparticles, but also tested microalgae species and cultivation conditions. In order to elucidate the action of very small gold/silver nanoparticles on halophile microalgae, experiments were carried out to cultivate green alga Dunaliella salina, in the presence of gold and silver nanoparticles. There have been used Au (PEG) and Ag(PEG) nanoparticles with the size of 5 nm in polyethylene glycol. Nanoparticles were supplemented to Ben-Amotz mineral medium with salinity of 120 g/l from the first day of cultivation. Concentrations of 0.054-0.108 mg/l AgNP had stimulatory effect. The content of biomass was 12-33% higher compared to control. A possible moderate toxic effect was set in the experimental variant with applying nanoparticles in concentration of 0.135 mg/l, which reduced biomass content with 15%. Doubling the concentration of nanoparticles to 0.27 mg/l has not altered biomass content of microalgal culture. It was investigate the impact of nanoparticles on biosynthetic activity of microalga. Thus, concentration of 0.054 mg/l AgNP enhanced the content of β-carotene in algal biomass with 33%. An increase of 20% of carotene content in biomass was also determined in variants with low concentrations of AgNP in cultivation medium. Therefore, no dependence between AgNP concentration in cultivation medium and microalgal culture response was established. The tested concentration of silver nanoparticles is not toxic for Dunaliella salina. It was established a concentration with stimulating effect on biomass production and β-carotene synthesis. In case of applying gold nanoparticles a stimulating effect has been revealed. Maximum accumulation of dunaliella biomass was determined by adding the concentration of 0.081 mg/l AuNP, for which biomass production has increased by 21%. Concentration of 0.27 mg/l AgNP, which was the maximum of applied doses, did not altered biomass accumulation, but resulted in a 20% increase of β-carotene content in biomass. The tested concentration of gold nanoparticles are not toxic for Dunaliella salina.. In conclusion, we can state that Ag (PEG) and Au(PEG) nanoparticles with 5 nm size, supplemented to growing medium, have no toxic effects and can be applied in cultivation technologies of microalgae Dunaliella salina as stimulants of carotenogenesis.