During recent years, zinc oxide nanoparticles (ZnO NPs) are utilized in different industrial sectors such as pharmaceutical and cosmetics industry, food and chemical industry. Zinc oxide NPs are a promising platform for use in biomedical research due to their anti-cancer, anti-bacterial properties. ZnO nanoparticles have gained interest in different applications based on their high stability, high specific surface area, nontoxicity, electrochemical activity. Evaluation and determination of nanotoxicity are important for the safe application and environmental risk assessment of nanoparticles. In spite of, ZnO NPs have been reported to possess low toxicity for diverse microorganisms. In the present study, the effect of ZnO NPs was evaluated in pigmented yeasts Rhodotorula gracilis CNMN-Y-03. In this paper are presented some experimental results of zinc oxide NPs-induced changes in yeasts cell colonies. It was established the effect of two types of nanoparticles ZnO <50 nm și ZnO <100 nm on dimension and morphological properties of Rhodotorula gracilis CNMNY- 03 strain depending on used concentration and contact duration. Commercially available ZnO nanopowder, (Sigma-Aldrich; particle size 50 and 100 nm) was used in the preparation of experimental solutions in concentrations from 1.0 to 70 mg/l. Research was effectuated on the solid fermentation medium YPD specific for yeasts [Aguilar-Uscanga et,al., 2003]. To obtain the colonies, yeasts cells of the control and experimental samples with NPs contact duration of 6 and 24 hours were seeded on solid YPD medium. The control culture is characterized by colonies 1-3 mm in size, R-shaped, with corrugated margins and intense coral color. Regarding the morphology of culture colonies in contact with nanoparticles ZnO <100 nm and ZnO <50 nm, some changes have been detected. There is also a significant difference in the dimension and color of colonies. It was observed that the color of the colonies of the experimental samples changes from intense to pale orange (specific for all concentrations ZnO nanoparticle concentrations <100 nm) and to pale orange and pink (specific for all concentrations of nanoparticle ZnO < 50 nm). That is supposed to be talked about the influence of nanoparticles on synthesis of pigments, in particular, of carotenoids. Determination of the diameter of colonies demonstrated a difference between experimental and control samples. The presence of nanoparticles of ZnO <100 nm and ZnO <50 nm slightly stimulated the growth of yeasts colonies. It can be mentioned that the presence of nanoparticles ZnO <50 nm contributes to increasing of the dimension of the colonies in a higher degree, than of ZnO <100 nm. In summary, yeasts colony morphology may be an indicator of nanoparticles action on microorganisms, this being an important adaptive process to overcome induced stress. The results demonstrated that ZnO NPs could influence the morphogenesis and depends on size of these particles. Furthermore, alterations in colony morphology may reflect increased resistance of yeasts.