In the Andean region, Philippines, and central Africa most guinea pigs are raised for meat production. Guinea pig meat is of increasing interest to researchers. One of the critical questions in meat production is to know when muscles convert to meat. The objective of this study was to describe the pH evolution in guinea pig muscles and to determine the establishment and resolution time of rigor mortis. Forty-eight guinea pig carcasses were divided into four groups: 12 male and 12 female of 3 month-old fattened animals, and 12 male and 12 female of 12 month-old reproductive animals. The pH was measured using a penetration probe in Longissimus thoracis, Quadriceps femoris, Triceps brachii and Psoas major muscles for 24 h, and rigor mortis was monitored during this time. The initial and final pH ranged between 6.56–7.00 and 5.97–6.27, respectively. Rigor mortis was established at ∼5 h and resolved at ∼15 h postmortem. The Psoas major was the muscle with lower initial pH and higher final pH, while no differences were found between the other muscles. Initial, evolution and final pH were not affected by the sex. No differences were found in the productive-reproductive status between males, whereas the older female guinea pigs presented higher pH in three muscles. In conclusion, in our test conditions final pH in guinea pigs remains high enough to permit microbial growth, which could affect the shelf-life of Guinea pig meat. Moreover, it is recommended to keep guinea pig carcasses in refrigeration until 15 h postmortem, when rigor mortis is resolved, and muscle-to-meat conversion finished. Management of these carcasses should be different depending if the animals belong to a productive or reproductive animal system. It is therefore necessary to chill guinea pig carcasses at least 15 h, to achieve a correct muscle-to-meat conversion.