The effect of thiamine Cl HCl and its synthesized VO2+, Fe(III) and Se(IV) complexes were examined for antimicrobial, anticancer, antiviral, anti-inflammatory, antioxidant and diabetic/antidiabetic activities and inhibitions of acetylcholine sterase, monoamine oxidase (MAO-A) and DNA cleavage inhibitions were carried out in vitro. The results revealed that selenium complex showed antibacterial activity against S. aureus, B. subtilis and E. coli and vanadium complex against S. aureus. The iron and selenium complexes acted as anticancer agent with IC50 equals 19.10 and 11.80 μg/ml respectively. Also, antiviral activity was tested by Se(IV) complex with moderate activity (++), while Fe(III) complex showed weak activity (+). DNA cleavage was examined by the three complexes at different concentrations (10- 0.01) mg/ml. It was found that all concentrations prevented the adverse effect of H2O2 on DNA fragmentation except (0.01 mg/ml) Se(IV) complex and (10 mg/ml) VO2+ complex. From sucrase, maltase and lactase activity results, it is suggested that VO2+, Fe(III) and Se(IV) complexes are effective anti-diabetic compounds. Inhibition of lipase activity was observed for VO2+ complex with IC50 = 2 × 10-4 mg/ml, while, for Fe(III) and Se(IV) complexes are 0.82 and 9.30 mg/ml, respectively. For antioxidant effect, significant drug concentration was recorded for Se(IV) and VO2+ complexes with IC50=0.082 mg/ml and IC50 =0.086 mg/ml, respectively, while Fe(III) complex with IC50=0.11 mg/ml. The results showed that AChE was inhibited by Fe(III), Se(IV) and VO2+ complexes with IC50 values, 0.011, 1.4 × 10-3 and 4 × 10-4 mg/ml, respectively. MAO-A was inhibited by Se(IV) and VO2+ complexes with IC50 values 0.45 and 3.2 × 10-4 mg/ml.