Abstract: By a direct computation one can check that all the threedimensional homogeneous spaces (pseudo-Riemannian manifolds with a threedimensional group of isometries) have a constant scalar curvature. I will explain why it is so, moreover, for any dimension. As a motivation we will mention the structure of curvature tensor of a maximal symmetric space. We will demonstrate that on homogeneous spaces also any scalar function of the metric tensor and its derivatives is constant. For curiosity we will present also Bianchi classification of threedimensional homogeneous spaces.