In this investigation, the effect of the annealing temperature for 6 hours with slow cooling (inside the furnace) in a pearlitic gray cast iron, on the tensile strength, ductility, hardness and microstructure has been studied. Cylindrical bars with a diameter of 15 mm x 200 mm in length were used, supplied by the Metallurgical Foundry and Related Services (FUMETSA), which were annealed at temperatures of 800, 850, 900, 950 and 1000 ° C for 6 hours with slow cooling (inside the furnace), and machined for the tensile test according to ASTM E8-98 standard and for the hardness test according to ASTM E-140 standard. The results show that by increasing the annealing temperature, the tensile strength decreases from 196.00 MPa for 800 ° C to 149.70 MPa for 1000 ° C. With respect to the ductility (% elongation), this increases with the increase of the temperature of annealing from 1.80% for 80...