Abstract The melt theological behaviour of short pineapple fibre reinforced low density polyethylene composite has been studied using a capillary rheometer. The influence of fibre loading, fibre length, and fibre treatment on the theology of composites was investigated. Studies were carried out in the temperature range of 125 to 145°C and shear rate of 016.4 to 5468 s −1. The melt viscosity was found to be increased with fibre loading. Various chemical treatments were made to improve fibre—matrix interfacial adhesion. Treatments based on poly(methylene)—poly(phenyl)isocyanate (PMPPIC), silane and peroxide increased the viscosity of the system due to high fibre—matrix interfacial interaction. Viscosity of the system decreased with increase of temperature. However, in peroxide treated composites viscosity is increased due to the crosslinking of composite at higher temperature. The fibre breakage during extrusion was analysed using optical microscopy. The morphology of the extrudates has been studied by optical and scanning electron microscopies. Master curves were generated using modified viscosity and shear rate functions that contain melt flow index as a parameter.