Short-range optical fiber communication is the key in intra and inter data center network, which is recently required significant improvement in signal processing speed because of the increasing data traffic of video streaming service and many other applications. The electro-optic (EO) polymer modulator is the promising device to be used in such fiber network application because of the advanced modulation performance with low driving voltage and high frequency response. However, previous EO polymer modulators have demonstrated the modulation at the wavelength of 1.55 µm (C-band) because of the optical loss limitation at shorter wavelengths of such as 1.31 µm (O-band). In this study, we fabricated silicon-organic hybrid modulator for O-band operation by replacing the pervious EO polymer. The modulator consists of the Mach-Zehnder interferometer Si waveguide with a hybrid slot and polymer phase shifter. The measured half-wavelength voltage product (Vπ·L) was 0.56 V·cm. We demonstrate 40 Gbps on-off-keying modulation, and show that the fabricated modulator is promising the higher bit rate signaling for O-band optical fiber communication application.