Two field experiments were carried out at the experimental Farm of the Faculty of Agriculture, Moshtohor, Benha university, Qalubiya Governorate, Egypt during the two successive seasons of 2010/2011 and 2011/2012, to study the effect of foliar application with bulk or nano-titanium dioxide (TiO₂ <10 nm) with three levels (0.01, 0.02 and 0.03 %) on the growth and nitrate content of lettuce (Lactuca sativa var. capitata cv. Great lakes) As a photocatalyst, nano-TiO₂ under light could cause an oxidation–reduction reaction. The nano-TiO₂ treatments have obvious effects on the improvement of growth and development in lettuce; however, bulk TiO₂ treatments have only little effects. It was demonstrated that nanoanatase TiO₂ (0.03%) could greatly improve growth (fresh and dry weight) and pigments of photosynthesis (β-carotene, chlorophyll a and b) of lettuce. The results also, showed that TiO₂ nano particles (0.03%) recorded the highest total yield (16.434 ton fed^-1) and the lowest content of nitrate in lettuce leaves (182.5 µg g^-1 DW) as an average in both seasons. Nano-anatase TiO₂ treatment could enhance growth, photosynthesis efficiency, activities of nitrate reductase and consequently decrease nitrate content in lettuce plants.