Intramuscular fat and collagen content are major factors affecting beef quality, but mechanisms regulating intramuscular adipose and connective tissue deposition are far from clear. Japanese Wagyu cattle are well known for their extremely high marbling. The objective of this study was to evaluate intramuscular fat (IMF) and collagen deposition in the muscle of Wagyu compared to Angus cattle. Animals were managed under the same condition and slaughtered at an averaging 585 ± 12.1 kg of body weight. Samples of sternomandibularis muscle were collected from Wagyu (n = 3) and Angus (n = 3) for molecular and histological investigations of adipogenesis and fibrogenesis. With exception of CCAAT enhancer binding protein β (C/EBPβ; P = 0.2864), the expression of the adipogenic markers, C/EBPα (P = 0.008), peroxisome proliferator-activated receptor γ (PPARγ; P = 0.028) and zip finger protein 423 (Zfp423; P = 0.047) in Wagyu were higher than in Angus muscle, which was consistent with higher IMF deposition in Wagyu (P < 0.05). In addition, more adipocytes and pre-adipocytes were detected intramuscularly in Wagyu cattle. Similarly, fibrogenesis was also enhanced in Wagyu, with a higher expression of fibroblast growth factor II (FGF2; P = 0.028), FGF receptor 1 (P = 0.030), transforming growth factor β (TGFβ; P = 0.028), collagen I (P = 0.012) and collagen III (P = 0.025). Similarly, Wagyu muscle had higher collagen content (P = 0.002) and lower collagen solubility (P = 0.005). In addition, muscle fiber diameter was larger (P < 0.0001) in Wagyu than in Angus cattle. These results clearly show that both IMF and collagen contents are enhanced in Wagyu cattle and more adipogenic cells are detected in Wagyu muscle, indicating intramuscular adipogenesis is enhanced in Wagyu compared to Angus muscle.