Garlic (Allium sativum) is one of the medically beneficial spices consumed by Sri Lankan people in different ways. The study aimed to determine the bioactive compounds and in vitro anticoagulant activity of aqueous and methanolic extract of raw, boiled, and honey fermented preparations of garlic. Different concentrations of aqueous and methanolic extract of raw, boiled, and honey fermented garlic were prepared by grinding different weights of garlic (2.5×10-3 kg for 500 mgmL-1, 1.25×10-3 kg for 250 mgmL-1, 0.25×10-3 kg for 50 mgmL-1 and 0.05×10-3 kg for 10 mgmL-1). For aqueous extract, the crude extract had been collected whereas for methanolic extract preparation, maceration had been done. In vitro anticoagulant activity was analysed using prothrombin time (PT) of pooled plasma diluted with different concentrations of garlic extract. Bioactive compounds in garlic extracts were analysed by Gas Chromatography-Mass Spectrometry. Methanolic extract of all 3 preparations and aqueous extract of honey fermented garlic had significantly prolonged PT at all concentrations compared to the control (p<0.05). Aqueous extract of raw and boiled garlic showed significant prolongation in PT only at high concentrations compared to the control (p=0.008). Prolongation in PT was increased with increasing concentration of garlic extract. Honey fermented garlic had the highest prolongation in PT compared to the other two preparations. Moreover, methanolic garlic extract exhibited the a higher prolongation in PT compared to aqueous garlic extract. The content of Dodecanoic acid methyl ester and Methyl tetradecanoate in boiled garlic extract was much higher than in raw garlic extract. Diallyl disulphide, Methyl thiourea and S-Methyl methanethiosulfinate were only found in aqueous raw garlic extract. Beta sitosterol was only detected in methanolic raw garlic extract. All three consumption methods of garlic have an inhibitory effect on blood coagulation. Honey fermented garlic is the most effective preparation for anticoagulant activity.