This invention discloses pure isolated Gymnemagenin from the hydrolysed extract of Gymnema sylvestre R.Br, leaves or its salts, ethers or esters of formula I a novel process for high yield isolation of Gymnemagenin from the hydrolysed extract of Gymnemasylvestre R.Br, leaves. Further, the invention discloses gymnemagenin or its water soluble salts having potent anti-diabetic and anti-hyperlipidaemic property and polymeric nanoparticles with high bioavailability of gymnemagenin in systemic circulation having potent anti-diabetic and anti-hyperlipidaemic activity.