Abstract: Background and Objectives: Turmeric, also known as Curcuma longa is being used as a traditional medicine throughout Asian countries from ancient time. The study aimed to quantify the concentration of curcumin in turmeric samples grown in four different geographical conditions such as Oman, Yemen, India (Asia) and Tanzania (Africa) and to investigate the effect of varying concentrations of curcumin on the in vitro anti-oxidant and anti-diabetic activity. Materials and Methods: Four types of turmeric samples were collected from Oman, India, Yemen and Tanzania. The curcumin content was determined in methanol and acetone extracts by UV-Vis spectrophotometer. Curcuminoids were also isolated, extracted and quantified from each sample. The in vitro anti-oxidant activity of turmeric samples were investigated by DPPH and Thiobarbituric acid assay methods while anti-diabetic activity was assessed by measuring the α-amylase inhibitory activity. Results: The results showed that the concentrations of curcumin, the biologically active constituent of turmeric, vary greatly among the four varieties. The methanolic extract of Omani variety contained the maximum curcumin content while the highest percentage yield of curcuminoids was isolated from the methanolic extract of Yemeni turmeric. It was found that methanol is the better solvent than acetone for the extraction of curcumin as well as curcuminoids. All turmeric extracts exhibited dose dependent anti-oxidant and anti-diabetic activity. Tanzanian sample showed the highest percentage inhibition of DPPH free radical and lipid peroxides (56.07 and 48.15%, respectively) while Yemeni sample possessed the highest anti-diabetic activity (38.06%). Conclusion: It may be concluded that curcumin content in turmeric depends upon the geographical location and climatic conditions where it is grown. The biological activity of turmeric depends upon its total curcuminoids content including curcumin.