Tetrafunctional urethane acrylates based on different types of diisocyanates were synthesized and were then used to prepare a series of five UV-cured hard coatings on polycarbonate (PC) substrate. The coating syrups consisted of the urethane acrylate with reactive hardening acrylic monomer (PETA; pentaerythritol tetraacrylate) and reactive diluent (hydroxyethyl acrylate). Their flexibilities and coating performance were investigated from the tribology results and transparency of the UV-cured hard coatings on PC substrate. The tribological properties showed better result when the content of PETA was increased in all of the UV-cured hard coating series. The surface hardness order of the UV-cured hard coating series was toluene diisocyanate (TDI)>toluene diisocyanate (IPDI)>4,4-methylenebis(phenyl isocyanate) (MDI)>4,4-methylenebis(cyclohexyl isocyanate) (HMDI)>4,4-methylenebis(cyclohexyl isocyanate) (HDI). However, their flexibilities demonstrated by critical bending radius showed the reverse order to the hardness results. All UV-cured hard coatings had a transmittance of over 89% in the visible wavelength range.