Nutritional supplements may impact vital physiological parameters differently, depending on season. Seasonal change in respiratory rate of homeotherms may be a physiological mechanism for heat dissipation/conservation (Furtado et al., 2008; Dzenda et al., 2015; Kumar et al., 2018). The aim of the present study was to determine the influence of season on the modulating role of ascorbic acid and L-carnitine, administered singly (100 mg/kg) or combined (50 mg/kg each), to captive African Giant rats (Cricetomys gambianus, Waterhouse) of either sex. The trap, capture, handling and management of the rats conformed to ethical guidelines (Gannon and Sikes, 2007; Cooper, 2008). The supplements were administered in drinking water, 3 hours before commencement of the experiment for each day. The respiratory rate of the rats (n = 10 per group per season) was counted in the morning, afternoon and evening for 3 days (1 week apart), each during the cold-dry (Dec/Jan), hot-dry (Mar/Apr) and early-rainy (May/Jun) seasons in Zaria, Nigeria. Data were subjected to one-way analysis of variance and Tukey’s post-hoc test. The mean ± SEM value of respiratory rate in control rats (administered only water) was highest (P < 0.01) during hot-dry (120.4 ± 2.97 breaths/min), followed by cold-dry (113.0 ± 3.57 breaths/min), and the least (P < 0.01) was recorded in early-rainy (79.29 ± 3.13 breaths/min) seasons. Overall, the respiratory rate was significantly (P < 0.01) lower in rats administered with ascorbic acid (95.43 ± 1.64 breaths/min) than in those given only water (103.2 ± 1.74 breaths/min) or L-carnitine (107.2 ± 1.84 breaths/min). Relative to control values, the respiratory rate was significantly (P < 0.01) lower and higher during the dry and early-rainy seasons, respectively in rats administered ascorbic acid only. The respiratory rate was significantly (P 0.05) alter the respiratory rate count. It was concluded that oral administration of ascorbic acid and L-carnitine modulated the respiratory rate in African Giant rats in a season-dependent manner. Ascorbic acid modulated the respiratory rate by decreasing and increasing the count to ameliorate its seasonal peak and nadir, associated with the hot-dry and early-rainy seasons, respectively. L-carnitine, on the other hand, raised the respiratory rate even during the hot-dry season, when the count was at its seasonal zenith. The administration of ascorbic acid may be more beneficial than that of L-carnitine in modulating respiratory rate across the seasons in the rats.