This paper presents the experimental results of an investigation on the mechanical properties of magnesium-treated nodular cast iron in the annealed and as-cast condition. The dynamic stress-concentration factors are compared with Neuber’s theoretical factors for hyperbolic notches, with Peterson’s results on steel, with Frocht’s photoelastic results, and with Grant’s data on flake cast iron and cerium-treated nodular iron. Fatigue results are shown for square and 45-deg V-shaped notches at speeds of 200 and 6000 rpm, as well as for various notch depths. The trend in size effect is indicated. Static damping capacities obtained from hysteresis loops in tension and compression are compared with torsional damping capacities and static damping capacities from bending.