The present invention relates to a cosmetic composition comprising: from 0.5% to 15% by weight, relative to the total weight of the composition of one or more fatty-chain silanes of formula (I) below and/or oligomers thereof: R1Si(OR2)z(R3)x(OH)y (I) in which formula (I): R1 represents a linear or branched alkyl or alkenyl group comprising from 7 to 18 carbon atoms, R2 and R3, which may be identical or different, represent a linear or branched alkyl group comprising from 1 to 6 carbon atoms, y denotes an integer ranging from 0 to 3, z denotes an integer ranging from 0 to 3, preferentially from 1 to 3 and better still equal to 3, and x denotes an integer ranging from 0 to 2, with z+x+y=3, one or more fixing polymers chosen from anionic, amphoteric and non-ionic fixing polymers. The invention also relates to the use of said composition for shaping and/or fixing keratin fibres, such as human keratin fibres and in particular the hair, and also to a cosmetic treatment process for keratin fibres using such a composition.
