Carbon Black filled Natural Rubber (CB-NR) is the most commonly used crystallizable elastomer for antivibratory applications in the automotive industry. For decades, uniaxial fatigue tests have been carried out for characterizing, understanding and modelling fatigue resistance of CB-NR. A typical result is the lifetime reinforcement observed for non-relaxing tension (Cadwell et al. 1940) as soon as 1940. Strain-induced crystallization (SIC) is generally assumed to be responsible for this reinforcement. In the late 2000s, special attention was paid to multiaxial fatigue in order to better meet the needs of industrial applications (Mars 2001, Saintier 2001, Le Cam et al. 2013), but often under relaxing loading. The present work aims at investigating the effect of non-relaxing multiaxial loadings on the fatigue lifetime reinforcement of CB-NR. For that purpose, pure torsion fatigue tests with different loading ratios have been performed with axisymmetric-shaped specimens made with the same material at 23 degrees C. A strong life reinforcement under non-relaxing torsion has been observed. Post-mortem SEM analysis carried out at the microscopic scale enabled us to identify damage mechanisms. Similarly to Le Cam et al. (2013) and Ruellan et al. (2018) in the case of uniaxial fatigue, the role of SIC in the multiaxial fatigue damage mechanisms has been determined and linked to the loading conditions by using a pseudo-Haigh diagram.