This study was conducted on bromelain from pineapple core (Ananas comosus [L] Merr). The crude enzyme gained from pineapple core extract was then fractionated by (NH4)2SO4 and ethanol in different concentration levels. Fractionation using 20-50% (NH4)2SO4 resulted in the highest specific activity of 89.32 U/mg with a purity level of 1.72 times. Further purification increased its specific activity to 120.83 U/mg with a purity level of 2.32 times. Fractionation using 20-50% ethanol obtained the highest specific activity of 184.79 U/mg with a purity level of 27.15 times. Bromelain fractions with the highest specific activity were tested in vitro for their activity as antiplatelet agents using PRP (Platelet Rich Plasma). The platelet aggregation percentage of ammonium sulfate fraction was shown as 17.12% with the platelet aggregation inhibition percentage of 81.56%. The 20-50% ethanol fraction showed the platelet aggregation percentage was 15.93% with the percentage of platelet aggregation inhibition of 82.83%. The fraction of bromelain with higher specific activity showed a higher aggregate antiplatelet activity.