A ball point pen ink composition having viscosity of at least 500 cps at 25° C. comprising 5-25% of slow evaporating organic solvent, 20-55% fast evaporating solvent, 16 to 36% of resin, 0.1 to 2% of structural viscosity imparting agent, 0.05 to 1% of polyvinyl pyrrolidone, 0.1 to 25% of lubricant, 3-25% of colorant, and 0.01 to 3% of amines/polyamines and/or 0.1 to 20% diols or polyols as associative thickening agents/additives; amines and/or diols or polyols capable of forming temporary bridging between silica particles at the same time forming associative coupling between amines itself and diols or polyol itself to obtain the ink composition having ultra low viscosity of about at least 500 cps and yet preventing leakage. The ink composition prevents leakage, bobbling and other defects associated with the prior art and at the same time gives pleasure while writing. The pen comprising, the above ink, is manufactured by the process of the invention.