This study aimed to design an adhesive biodegradable polymer layer on the surface of titanium (Ti) implants for enhanced surface bioactivity. To this end, a coating of magnesium-particles doped biodegradable polyurethane (PU) was introduced as a composite layer on Ti surfaces using a simple spin coating technique. The coating’s performance and characteristics were investigated in terms of the surface topography, composition, surface roughness, wettability, adhesion and electrochemical behavior of composite coatings on untreated (polished) and alkaline treated Ti substrates. Interestingly, the Ti samples coated with the composite layers showed superior corrosion resistance compared to the uncoated samples. Additionally, the coating on alkali-treated Ti surfaces demonstrated enhanced adhesion (5B, measured by cross-cut test) compared to the coating on untreated Ti (1B), indicating the vital role of the alkaline-treatment step. A composite thin layer coated on alkaline-treated Ti enhanced osteoblastic-like (MC3T3-E1) cellular adhesion and cell proliferation and was found to support osteoblastic differentiation compared to uncoated alkaline-treated Ti. Surface modification of alkaline-treated Ti with a biodegradable Mg-particles/PU thin layer appears to be a promising strategy for developing surface bioactivity of orthopedic devices.