The effects of rosmarinic acid (RA) immobilized onto a screen printed carbon electrode (SPCE) were investigated for the development of an NADH sensor and an ethanol biosensor. RA was electrodeposited on SPCE by cyclic voltammetry. Scan rate and number of cycles were optimized for electrodeposition. RA modified SPCE (SPCE/RA) was found to facilitate the electrocatalytic oxidation of NADH by the action of RA as a natural antioxidant mediator. pH and working potential were optimized for the determination of NADH with the developed SPCE/ RA sensor. They were found as 7.25 and 0.25 V, respectively. Alcohol dehydrogenase (ADH) enzyme was immobilized onto this sensor to prepare a disposable amperometric ethanol biosensor. NAD(+) was used as a cofactor for ADH. pH, working potential, amounts of ADH and NAD(+) were optimized for the developed biosensor. The optimum values were found as 7.75, 0.20 V, 250 unit and 7 mM, respectively. Analytical characterization parameters for ethanol analysis were determined. The sensitivity, linear range, limits of detection and quantification were 1.36 mu A mM(-1), 23.71 mu M-1000 mu m, 7.1 mu M and 23.7 mu M, respectively. The repeatability, operational stability and storage life studies were performed. RA is found to enhance the operational stability of the biosensor. The developed biosensor has been tested on a few commercial alcoholic drinks for the analysis of their ethanol contents.