A new Yb-based compound YbRhSb with the orthorhombic -TiNiSi-type structure has been synthesized. The magnetic-susceptibility, magnetization, and specific-heat (Cp) measurements of single crystals revealed a ferromagnetic transition at TC = 2.7 K. An extrapolation of the Cp/T data below 1 K yields 370 mJ/mol K2 as the value, and the magnetic entropy reaches only 0.25R ln 2 at TC. The spontaneous moment is unusually small, 3×10–3µB/Yb for B||b, while the magnetization increases to 1.4µB/Yb when the field of 15 T is applied along the a axis. We ascribe the weak ferromagnetism to a canted antiferromagnetic structure based on the observation of a metamagnetic transition and the decrease of TC with the increase of magnetic field.