High-quality c-axis oriented SBN60 thin films on MgO(001) substrates have been obtained by the sol-gel process, the transverse electrooptic coefficients r51 of the SBN60 without K-doped and K-doped (with the K+/Nb5+ molar ratio of 1/3) SBN60 thin films were measured as 37.6 pm/V and 58.5 pm/V respectively. The transverse coefficient of the SBN60 films was shown to increase with the K ions doping. Mach-Zehnder type waveguide modulators made of SBN60 thin films were designed. Electrooptic modulation has been demonstrated with the half-wave modulation voltage Vπ=16 V for SBN60 and that of Vπ=10 V for the K-doped SBN60 at 633 nm wavelength. The half-wave modulation voltage was demonstrated to be decreased with the K ion doping.