Trehalose (α-D-Glucopyranosyl-1, 1-α-D-glucopyranoside; Molecular formula: C12H22O11) is a non-reducing disaccharide formed through a 1-1 alpha bond linking two glucose moieties. Trehalose (Tre), a non-reducing disaccharide of glucose and is considered as one of the most effective in stress protectant in plants. Keeping this fact in mind, it was hypothesized whether foliar application of Tre can affect the secondary metabolites particularly, phenol contents and other physiological and biochemical parameters in Ocimum tenuiflorum L. (Holy basil). This study was performed using a pot experiment with a simple randomized design. Plant’s secondary metabolites are of immense value in the pharmaceutical, perfume, cosmetic and other industries. Trehalose has been demonstrated as a plant growth regulator, plays a pivotal role in growth and various metabolic processes of plants. The present study is aimed to elucidate the effects of Tre through foliar application on O. tenuiflorum. Various concentrations of Tre viz. 0, 5, 10, 20, 40 mg L-1 were applied on the plants five times in crop duration with an interval of one week. Biochemical parameters were studied spectrophotometrically. Chlorophyll fluorescence or photochemical quenching was determined using Junior PAM chlorophyll fluorometer. The effect of leaf-applied Tre was found significant for all growth and physiological attributes of the studied plant. Of the tested concentrations, Tre at 20 mg L-1 has proved the optimum concentration for overall performance of the medicinal herb.