This study was conducted to investigate the effects of different essential oil-based organo-nanoparticle (NP) applications on morphological development and antioxidant defense system of tomato (Solanum lycopersicum L.) plants. Five treatments were evaluated: Control (NP0), mint [p(MO)], sesame [p(SO)], onion [p(OO)] and garlic [p(GO)] derived organo-nanoparticles. Plants were grown under controlled conditions and morphological parameters such as number of leaves, plant height, stem diameter, shoot and root fresh and dry weights were measured. In addition, biochemical analyses including catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), malondialdehyde (MDA), total phenol content, and DPPH radical scavenging activity were performed. The results indicated that NP treatments had significant effects on plant growth and physiological responses. Particularly, sesame-based nanoparticles [p(SO)] provided the most favorable outcomes in terms of morphological growth parameters (e.g., highest plant height, number of leaves, and shoot biomass) and antioxidant defense components (e.g., highest SOD and phenol content, and lowest MDA levels). Garlic-based nanoparticles also showed notable performance in stem development and APX activity. These findings demonstrate that the application of essential oils in nanoparticle form can promote plant growth and reduce oxidative stress in tomato plants. It can be concluded that essential oil-based nanoparticle systems hold potential as natural biostimulants in agricultural production. However, further research is needed to assess their long-term efficacy and environmental impact under field conditions.