Although favorable effects of Selenium nanoparticles (SeNPs or nSe) in tomato have been reported, research has concentrated on stress alleviation and disease management. From the above it is noticeable that the effect of NPs varies greatly depending on the model plant, nanoparticle (concentration, size, shape), and application (foliar or drenching). For this reason, the objective of this study was to investigate the impact of biostimulating tomato plants under no stressor conditions (Solanum lycopersicum cv. ‘Pomodoro’ L.) with SeNPs on morpho-physiological and fruit quality parameters. Three doses of Selenium nanoparticles (5, 15, and 30 mg L⁻¹), and a control were applied via a foliar application after transplanting. The results indicate that a 5 mg L⁻¹ SeNP treatment improved the growth and yield of the tomato, with the exception of the root length and leaf weight. Moreover, all doses modified the evaluated physiology, bioactive compounds, and fruit quality parameters. This research helped in understanding the SeNPs’ effect on tomato plants in greenhouses under a no stressor condition.