AbstractThe iodine which is added to an aqueous amylose solution is bound only partly by the amylose while forming the blue complex and partly remains free. The equilibrium normality of the free and the bound iodine at half‐saturation of amylose by iodine is designated as [If]vand [Ib]w, respectively. The stability of the poly iodine chain formed within the axis of amylose helices depends on its length, i.e., indirectly on the DP of the amylose helices: the greater this stability, the lower the [If]vvalue. The amylose molecule consists of helical segments. Such a molecule may behave as a random coil. The average length of the helical segments in freshly prepared amylose‐iodine complexes depends on temperature, pH, iodide concentration, the presence of other complex‐forming agents, and the DP of the amylose. This latter factor is investigated in the present paper. By the aid of an automatically recording photometrictitrating device the coherent values of [Ib] and [If] were determined. Plotting these values againstDPnfor mechanochemically degraded as well as for periodateo‐xidized amyloses resulted in curves consisting of two linear sections. The break of the curves occurred betweenDPn110 and 130. It was concluded that belowDPn= 100 the DP of helical segments (=sDPn) is identical to theDPnof the total molecule, i.e., the molecule consists of only a single, relatively stiff helix. Above this limit the molecule contains several helical segments. TheDPof these helical segments can be calculated as follows:sDPn= 141.1 − 10.2 × 105[If]v. This equation is considered to be valid for 0.5–0.6 mg. amylose in 100 ml. 0.1NHCl at 20°C., λ = 650 mμ, euuvet diameter 3.4 cm., the feed rate of the iodate‐iodide titrating solution (in acid medium resulting in a 5 × 10−3NI2solution with a molar iodide to iodine ratio of 1.5) is 0.4ml./min. Amylose molecules of, e.g.,DPn= 1380 consist of an average of 11.4 segments having aDPof about 120 and consisting of an average of