  We present the first measurements of magnetisation and Raman light scattering
on $\alpha'-NaV_2O_5$ single crystals. Below 34 K, we observe a pronounced
isotropic decrease of the susceptibility indicating the opening of a spin gap.
The transition temperature is slightly field dependent. Raman experiments
reveal a crystallographic distortion at the transition. Our results clearly
establish $\alpha'-NaV_2O_5$ to be the second inorganic spin-Peierls system.
