Class of 2017 Abstract / Objectives: Evaluate thymoquinone (TQ) and thymol (THY) inhibitory activities against α-glucosidase enzyme by using an in vitro assay and determine the IC50 (concentration of TQ/THY to inhibit 50% of maximum enzyme activity). Methods: Various concentrations of thymoquinone and thymol were incubated, separately, with one concentration of the substrate - p-nitrophenol-α-D-glucopyranoside (PNPG) (<<Km) in presence of α-glucosidase enzyme. A positive and a negative control consisting of acarbose, and buffer, respectively, were included in the incubation as well. The incubation time was set at 30 min in a 37 °C controlled water bath. The enzyme activity was determined by detecting and quantitating the levels of p-nitrophenol using a spectrophotometer set at 405 nm. The percent inhibition exhibited by any studied drug was calculated as shown in equation 1. % inhibition = Absorbance Substrate Alone – Absorbance of Substrate + Inhibitor Absorbance Substrate Alone Results: Results of the in vitro incubation of thymoquinone, thymol and acarbose revealed “statistically” significant inhibition of -glucosidase (p<0.05). At 400 g/ml, thymoquinone inhibited the enzyme activity by ~52 % whereas the enzyme inhibition by thymol and acarbose were calculated to be ~84% and 57%, respectively. IC50 were tentatively determined although the maxima inhibitions of the inhibitors were not reached fully. IC50s were calculated as 234 μg/ml, 304 μg/ml and 157 μg/ml for each of thymoquinone, thymol and acarbose, respectively. Conclusions: Thymoquinone and thymol do exhibit antagonistic pharmacological activity against α-glucosidase.