In this paper, we consider projective deformation of the geodesic system of Finsler spaces by holonomy invariant functions: Starting by a Finsler spray S and a holonomy invariant function P, we investigate the metrizability property of the projective deformation S = S −2λPC. We prove that for any holonomy invariant nontrivial function P and for almost every value λ ∈ R, such deformation is not Finsler metrizable. We identify the cases where such deformation can lead to a metrizable spray: in these cases, the holonomy invariant function P is necessarily one of the principal curvatures of the geodesic structure.2010 Mathematics Subject Classification. 53C60, 53B40, 58B20, 49N45, 58E30.