The Rendement Napole gene (RN) consists of a mutation at the γ3 subunit of AMP-activated protein kinase (AMPK) in pigs. AMPK works as an energy level sensor and controls numerous cellular pathways. The study aimed at identifying the differences in microstructure occurring between the normal porcine meat and porcine meat encoded by the RN gene. Using molecular techniques 194 commercial pigs were sampled to determine their genotypes. Meat from the semimembranosus muscle was examined using optic (OM) and transmission electron microscopy (TEM). The genotypes rnI/rnI, rnV/rnV, rnV/rnI, RN/rnV and RN/rnI were identified. OM revealed broadening of the sarcoplasmic space in RN animals, while TEM showed disordering of muscle fibres and alteration of the sarcomeric structure. Mitochondrial degradation was found in both RN and normal animals,however, the morphological changes observed seemed to be caused by the mutated AMPK.