Polyalkylpiperidines of formula I, ##STR1## wherein R.sup.1 is H or lower alkyl, R.sup.2 is H, O or a monovalent organic residue and Z is a divalent aromatic residue, are excellent light stabilizers for plastics. These compounds can be prepared from the according 4-oxopiperidines by Wittig-Horner reaction with diphosphonates of the formula IV,(ro).sub.2 (o)p--ch.sub.2 --z--ch.sub.2 --p(o)(or).sub.2 ivwherein R denotes lower alkyl, and subsequent hydrogenation of the resulting diolefines. The compounds of formula I are especially suitable for the stabilization of polyolefins, styrene polymers and polyurethanes.