A non-erasable ball point ink composition for a writing instrument, comprising an isocyanate free thermoplastic polyurethane resin, an organic solvent and a colorant, wherein the colorant is a dye or a pigment, wherein the pigment is selected from the group consisting of organic pigments, metallic pigments, phosphorescent pigments, fluorescent pigments, photochromic pigments, thermochromic pigments, iridescent pigments, liquid crystal pigments, carbon black pigments, inorganic pigments and pearlescent pigments, wherein the said inorganic pigments are selected from iron oxide pigments, chromium oxide pigments, chromate pigments, cadmium pigments, ultramarine pigments which are sodium aluminium sulfo-silicates having the general formula Na 8 Al 6 Si 6 O 24 S (2-4) or iron blue pigments which consist of alkaline iron salts of iron-cyanogen hydrogen acid which contains divalent as well as trivalent iron, wherein the said pearlescent pigments are selected from metallic lustre pigments which consist of a mica nucleus covered with an iron oxide layer and wherein the organic solvent comprises one of alcohols, polyols, polyol ethers, ketones, esters, pyrrolidones, lactones, hydrocarbons and mixtures thereof and wherein the thermoplastic polyurethane resin and organic solvent form a homogeneous solution and the colorant is soluble in said homogeneous solution or dispersed in said homogeneous solution. wherein the colorant is a dye or a pigment, wherein the pigment is selected from the group consisting of organic pigments, metallic pigments, phosphorescent pigments, fluorescent pigments, photochromic pigments, thermochromic pigments, iridescent pigments, liquid crystal pigments, carbon black pigments, inorganic pigments and pearlescent pigments, wherein the said inorganic pigments are selected from iron oxide pigments, chromium oxide pigments, chromate pigments, cadmium pigments, ultramarine pigments which are sodium aluminium sulfo-silicates having the general formula Na 8 Al 6 Si 6 O 24 S (2-4) or iron blue pigments which consist of alkaline iron salts of iron-cyanogen hydrogen acid which contains divalent as well as trivalent iron, wherein the said pearlescent pigments are selected from metallic lustre pigments which consist of a mica nucleus covered with an iron oxide layer and wherein the said inorganic pigments are selected from iron oxide pigments, chromium oxide pigments, chromate pigments, cadmium pigments, ultramarine pigments which are sodium aluminium sulfo-silicates having the general formula Na 8 Al 6 Si 6 O 24 S (2-4) or iron blue pigments which consist of alkaline iron salts of iron-cyanogen hydrogen acid which contains divalent as well as trivalent iron, wherein the said pearlescent pigments are selected from metallic lustre pigments which consist of a mica nucleus covered with an iron oxide layer and wherein the organic solvent comprises one of alcohols, polyols, polyol ethers, ketones, esters, pyrrolidones, lactones, hydrocarbons and mixtures thereof and wherein the thermoplastic polyurethane resin and organic solvent form a homogeneous solution and the colorant is soluble in said homogeneous solution or dispersed in said homogeneous solution. <EOS>