2 230 809 5 production was impossible because of too much amount of fluffs______________________________________ from table 1 fig1 was prepared it was found that in order to obtain fibers having physical properties 250 kgf mm 2 or more in tensile strength and 75 tonf m 2 or more in modulus of elasticity it was preferable to carry out graphitization treatment with a stretching ratio of from 5 to 7 2 infusiblized fibers prepared similarly as in example 1 were subjected to carbonization treatment at a temperature in the range of 700 u00b0 c to 2700 u00b0 c and carbon fibers having different modulus of elasticity as shown in table 2 were obtained table 2______________________________________ tensile modulus oftreatment strength elasticityno temperature u00b0 c kgf mm sup 2 tonf mm sup 2 example______________________________________1 700 30 3 fig2 1000 114 9 fig3 2200 279 42 fig4 2700 285 70 fig5 ______________________________________ further graphitized fibers having properties indicated in fig2 to fig5 were obtained by the graphitization treatment carried out at a temperature of 2800 u00b0 c for 30 second while stretching fig6 which shows most preferable range of stretching ratio was prepared from the results of fig1 to fig5 from fig6 it has been concluded to be preferable that when a modulus of elasticity of carbon fibers is 2 tonf mm 2 or more and 10 tonf mm 2 or less graphitization is to be carried out with a stretching ratio s which satisfies the condition of.