Semiconducting silicides are highly promising materials for applications in thermoelectric, photovoltaic and optoelectronic devices. Here, using ab-initio density functional theory, the lattice dynamics, dielectric properties, Infrared (IR) refletivity and Raman intensity spectra of Nowotny chimney-ladder semiconducting silicide Ru2Si3 are investigated. The zone-center phonon mode frequencies are found to be in the range 80-510 cm(-1). The Born effective charge tensor, oscillator strength and Infrared activity is found to largest for the mode with frequency 422 cm(-1) which is primarily contributed by displacements of Si atoms. The largest Raman activity is obtained for mode with frequency 479 cm(-1) which is also dominated by vibrations of Si atoms. Modified Becke-Johnson (MBJ) exchange potential is used to compute the band gap of Ru2Si3 which improves the band gap by similar to 8% as compared to that obtained using LDA. The computed Infrared reflectivity and Raman intensity spectra are expected to provide benchmark first-principles theoertical results for comparison with the experiments.