AbstractThe room‐temperature grafting of polyacrylonitrile (PAN) onto guaran (guar gum) in 2.5 × 10−3M aqueous sols or aqueous‐methanolic suspensions, initiated by (NH4)4Ce(NO3)6in 1M HNO3, leads to PAN‐branched polysaccharides with graft contents of 11 – 53%. Main chain degradation by treatment with boiling aqueous HCl results in detachment of the PAN side chains, for which number‐average molecular masses of ca. 15000 – 48000 are determined viscometrically with the aid of the known Mark‐Houwink relationship (K = 3.92 × 10−4, a = 0.75). Grafting frequencies are in the range of 0.004 – 0.012, equivalent to an average of 80 – 250 non‐grafted repeat units for every singly grafted unit in the guaran main chain. The graft copolymers are of interest as precursors of carboxyl‐functionalized, water‐soluble polysaccharides to serve as polymeric micronutrient and dr