A chlorinated colorless polyolefin, preferably a chlorinated colorless isotactic polypropylene, soluble in carbon tetrachloride and having a chlorine content of from 60% to 70% by weight and an average degree of polymerization of from 2000 to 6000, produced by chlorinating polyolefins having a degree of polymerization of from 2000 to 20,000 in suspension or solution or in suspension and solution at 40 to 60.degree. C. in the presence of a halogen transfer agent, a chlorination catalyst and from 0.2 to 0.5% by weight, based on polyolefin, of at least one compound corresponding to the general Formula (I):h.sub.2 n--r--nh>.sub.n H (I)in which R represents the ethylene, propylene or butylene group and n=1-6.