The development of high-performance bio-based greases is crucial for replacing conventional mineral oil-based products and advancing green sustainability. Herein, a fully bio-based grease was successfully synthesized exclusively from renewable feedstocks: castor oil and chitin. The base oil was modified castor oil obtained via one-step transesterification catalyzed by tetrabutyl titanate, while chitin served as the thickener. The optimal grease-forming reaction was achieved under mild conditions (25°C, stirring at 800 rpm, 120 min), followed by intensive mechanical processing using a triple-roller mill. Systematic characterization demonstrated that the resulting bio-grease exhibits comparable or superior physicochemical properties and thermal stability to traditional metal soap-based greases. Tribological tests showed that its wear scar diameter(WSD) was 0.58 mm, and the average friction coefficient(COF) was 0.0882, comparable to conventional mineral oil metal soap-based greases. Notably, it showed enhanced high-temperature viscosity retention, improved shear resistance, and greater mechanical stability. This study presents a viable and sustainable pathway for next-generation lubricants, featuring a fully bio-based composition, a streamlined and scalable synthesis under mild conditions, and minimal waste generation.