The influence of Main Sequence stellar rotation on horizontal branch stars and on RR Lyrae pulsational properties is studied. Synthetic HB's are computed for a wide range of original chemical compositions taking into account evolutionary effects based on Fusi Pecci-Renzini's evolutionary scheme. Theoretical properties of RR Lyrae pulsators are discussed: it is shown that main sequence rotation is able to induce in HB structures sensitive variations, so that some fundamental relations obtained in the classical frame (i.e., no rotation) have to be released. Consequences on the decodification of observational properties in galactic globular clusters are discussed.