We report the discovery of a new slowly pulsating B star, with the largest number of detected frequencies to date by more than a factor of 3, based on 37 days of MOST (Microvariability and Oscillations of STars) satellite guide star photometry. The star HD 163830 (V = 9.3, B5 II/III) varies in 20 detected frequencies in the range 0.035-1.06 day(-1) (0.4-12.3 mu Hz) with amplitudes from 0.7 to 7.6 mmag (with a signal-to-noise ratio from 4 to 41). Eighteen of these frequencies are consistent with low-degree, high-order nonradial g-modes of seismic models of an evolved 4.5 M-circle dot star. We are unable to identify one unique model due to lack of mode identifications. The lowest two frequencies may be associated with the rotation of HD 163830, but firm proof of this must await future spectroscopic data.