Natural rubber composites reinforced with pineapple leaf fibre (PALF) were investigated using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy-Dispersive Spectroscopy (EDS). Mechanical properties, including tensile strength, elongation at break, impact resistance, hardness, flexural strength, and elastic modulus, were evaluated for composites containing 0–4 g PALF. FTIR revealed a shift in O–H stretching from 3350.9 cm⁻¹ (0 g) to 3306.1 cm⁻¹ (4 g), indicating enhanced hydrogen bonding and fibre–matrix adhesion. The disappearance of the C≡C/C≡N band in reinforced samples confirmed chemical stabilisation and fibre incorporation. SEM showed smooth morphology in unreinforced rubber, while PALF composites exhibited rougher surfaces with embedded fibres, alongside regions of fibre pull-out and agglomeration. EDS confirmed increased carbon and oxygen content in reinforced samples, consistent with cellulose incorporation. Tensile strength and elongation at break increased to maxima at 2 g PALF (11.80 MPa, 386%) before declining at higher loadings due to agglomeration. In contrast, impact resistance, hardness, flexural strength, and elastic modulus increased monotonically, with impact resistance reaching 0.90 MPa at 4 g. Moderate PALF loading (≤2 g) provides optimal strength–flexibility balance, while higher contents enhance rigidity at the expense of elasticity, demonstrating PALF’s potential as a sustainable rubber reinforcement.