This study aimed to investigate the effect of foliar spraying of seaweed extract as a bio-stimulant throughput on some quantitative and qualitative properties of tomato. The experiment was carried out in factorial form within the format of complete randomized block design with four replications during 2014 in a mechanized greenhouse belonging to Gol Azin Maghsoud Company in Tus Industrial Estate in Mashhad. The study treatments were as follows: seaweed extract in four (distilled water) levels of 1, 2, and 3 ml per 1000L (of seaweed extract under the trademark of Stimplex) and verities in three levels of Hungarian Mobil, Dutch Mobil, and Super Queen. The results indicated that the concentration “2 ml per 1000 L” had a significant effect on the performance, antioxidant percentage, acidity, and vitamin C content of tomatoes. No significant difference was evidenced in terms of the other studied traits but the differences were considerably significant between the varieties.