The recycling of plastics and the incorporation of bio-fillers in the plastic industry are processes currently gaining momentum due to their significance in sustainable development and carbon footprint reduction. In this investigation, a biocomposite was fabricated using recycled polypropylene (RPP) reinforced with oyster shell (OS) particles. The introduction of OS bio-fillers is aimed to mitigate plastic shrinkage during the injection molding process, with two different proportions employed: 10wt.% and 30wt.%. The biocomposite was characterized thermally and mechanically. Thermal analysis by TGA showed that the bio-fillers increased the degradation temperature of the recycled polypropylene biocomposite. Mechanical assessments demonstrated an enhancement in polypropylene stiffness by 10.4% and microhardness by 21.1%, albeit at the cost of reduced ductility. Conversely, the tensile strength and impact resistance decreased slightly with the incorporation of OS particles in RPP. Dynamic mechanical analysis indicated an improvement in the storage modulus up to 1.45 GPa of the biocomposite with the reinforcement of OS particles. These findings underscore the potential for integrating recycled polypropylene with natural reinforcements, aligning with the global pursuit of environmentally sustainable materials in diverse industrial applications.