Dietary flavonoids possess distinct antioxidant and anti-inflammatory properties and may also regulate mitochondrial function. With advancing age and physical inactivity, skeletal muscle mitochondrial function is compromised. No studies have investigated the potential for flavonoids to modulate mitochondrial function in young and replicatively ‘aged’ C2C12 skeletal muscle cells. Therefore, the objective of this study was to examine the impact of acute dietary flavonoid treatment on mitochondrial function in control (P5-8) and replicatively aged (P49-51) C2C12 myoblasts and myotubes. Undifferentiated myoblasts (0-24 h) and differentiated myotubes (96-120 h) were treated with flavonoids (Quercetin, Q; Epigallocatechin Gallate, EGCG; and (-)-Epicatechin, EPI) at four doses (0, 1, 5 and 10 µM). After 24 h treatment, mitochondrial bioenergetics were examined using an extracellular flux analyser (Seahorse XFe96). Mitochondrial and antioxidant related gene expression in young myoblasts was also determined by RT-PCR in response to Q, EGCG and EPI treatment (0, 5 and 10 µM) over 24 and 48 h. PCG1a gene expression was augmented 2.2- and 1.2-fold over control at 48 h by 5 and 10 µM EPI (P = 0.011) and EGCG (P = 0.030), respectively. Similarly, at 48 h, 10 µM EPI and 5 µM EGCG increased SOD2 expression by 1.8-fold (P = 0.018) and 2.2-fold (P = 0.010), respectively vs control. A significant main effect of age on basal respiration (BR), ATP production, proton leak (PL) and coupling efficiency (CE) was evident in myoblasts (P < 0.05), with aged cells demonstrating 35, 43, 27 and 6 % higher values over control, respectively. Compared to untreated myoblasts, BR was ~30% lower in EPI treated (1 and 5 µM) aged myoblasts (P < 0.05). EPI treatment (10 µM) also lowered PL in aged myoblasts vs. untreated control (P = 0.020). In myotubes, there was a significant main effect of age (P < 0.005) on maximal respiration, PL, ATP generation, spare respiratory capacity % and CE, with young controls exhibiting 190 % greater (P < 0.001), 38 % lower (P = 0.090), 20 % higher (P = 0.534), 62 % higher (P < 0.001) and 13 % higher (P < 0.001) values over aged controls, respectively. There was generally no significant effect of flavonoid treatment, although, EGCG (1 µM) lowered BR and PL in comparison to untreated aged myotubes (P < 0.05). In summary, we demonstrate flavonoids may upregulate the transcription of mitochondrial associated genes in myoblasts. Moreover, we show flavonoids may offer therapeutic potential in aged skeletal muscle cells via actions on mitochondrial bioenergetics. Our findings also suggest replicative ageing has divergent effects on mitochondrial function in myoblasts and myotubes. Whilst aged myoblasts show no evidence of mitochondrial deficiency over control cells, aged myotube bioenergetics seem impaired following differentiation vs unaged control myotubes.