A natural rubber (NR) with a conventional sulfur cure system and a ratio of sulfur/accelerator (Omega) equal to 3 was investigated. The network structure of the NR during vulcanization was analyzed using a model of rubber elasticity based on the tube concept, which was applied to the treatment of the stress-strain measurements. The influence of cure time and temperature on the chemical crosslinks density was analyzed. The values were compared with those obtained by means of an equilibrium volume swelling measurement. The differences between samples of NR cured with Omega = 3 and 1.5 were analyzed.