An analytical and experimental study of nanofilm aluminum (Al) for ultra-high dynamic range surface plasmon resonance (SPR) biosensor is presented in this article. A thin film of 16 nm Al is proposed for metallic sensing layer for SPR sensor. For the protective layer, a 10 nm of gold (Au) layer was configured on top of Al as a protection layer. This ultra-high dynamic range of SPR biosensor reached the bulk refractive index sample limit up to 1.45 RIU. For the analytical study, with the assumption of anisotropic refractive indices experiment, the dynamic range showed a refractive index value of around 1.58 RIU. The refractive index value limit achieved by the proposed sensing design is potentially implemented in various applications, such as in chemical detection and environmental monitoring study with high refractive index solution sample. The experimental results are presented as a proof-of-concept of the proposed idea.