Plant secondary metabolites constitute the most important class of natural products with diverse and valuable chemical properties and biological activities. Artemisinin, isolated from Artemisia annua L., is potentially a drug that could be effective against multidrug-resistant strains of the malarial parasite, Plasmodium. Salicylic acid (SA) acts as a potential plant growth regulator and plays an important role in regulating a number of plant physiological and biochemical processes. The present study was conducted to assess the alterations in plant growth, photosynthetic capacity, enzyme activities, and content and yield of artemisinin in Artemisia annua L. in response to foliar application of SA. Four levels of SA (0.00, 0.25, 0.50, and 1.00 mM SA) were applied on the above-ground plant parts. Plant height and dry weight were altered significantly as the level of SA increased. Besides, application of SA positively improved chlorophyll and carotenoid contents. Furthermore, significant enhancement in net photosynthetic rate (31.7%) and the activity of nitrate reductase (17.2%) and carbonic anhydrase (10.9%) was noticed as the level of SA was increased from 0.00 to 1.00 mM SA. Most importantly, the content and yield of artemisinin was positively regulated by the SA. In comparison to no SA application (control), SA at 1.00 mM increased the content and yield of artemisinin by 25.8 and 50.0%, respectively.