bath as described in example 1 then the fibers were introduced into the second coagulation bath consisting of a 60 wt aqueous solution of dimethylacetamide at 35 u00b0 c for attempting 5 0 fold stretching in the bath but the filaments were broken and fluffed in the second coagulation bath resulting in interruption of spinning fig1 and 2 show sem surface scanning electron microscope photographs for example 1 and comparative example 1 respectively an acrylonitrile fiber bundle for a carbon fiber precursor according to this invention shows a good convergence and high denseness and thus a small load in drying step therefore even a fiber bundle with a total size of 33 000 dtex or more can be effectively produced without reduction in a spinning rate furthermore the fiber bundle according to this invention shows a total size of 33 000 dtex or more so that in molding process using carbon fibers prepared from the bundle of precursors a process of aligning multiple carbon fibers can be omitted and thus the problems of complexity and a higher cost in molding production can be solved an acrylonitrile fiber bundle for a carbon fiber precursor according to this invention shows the iodine adsorption property that is the amount of iodine adsorbable to the fiber is 0 5 to 1 5 wt it can be therefore calcimined to give a very strong carbon fibers with a good convergence as described above and showing good spreadability in pre preg production using the carbon fibers furthermore a process for producing an acrylonitrile fiber bundle for carbon fiber precursors according to this invention can readily and stably produce the above acrylonitrile fiber bundle showing good denseness a small drying load and a good convergence which is a.