Background: Diabetes patients are more likely to experience foot infections, which are extremely morbid and raise the possibility of lower limb amputation. The clinical symptoms and indications of local inflammation are used to diagnose diabetic foot infections (DFI). Objective: This study aimed to evaluate procalcitonin/Lactate ratio as a diagnostic marker for osteomyelitis and soft tissue infection in diabetic foot ulcers. Patients and methods: This case-control study was carried out on 112 diabetic patients attending to Diabetic Foot Outpatient Clinic, Zagazig University. Patients were divided into 4 groups: Group (1) included patients with T2DM without foot complications, group (2) patients with non-infected diabetic foot ulcer (NIDFU), group (3) that included infected diabetic foot without osteomyelitis and group (4) Infected diabetic foot with osteomyelitis. Full clinical examination, routine and metabolic investigations were done. Procalcitonin, lactic acid level and procalcitonin/lactate ratio were measured for all subjects. In addition, MRI on bone of infected diabetic foot groups was done. Results: A statistically significant increase in serum procalcitonin, lactic acid level and procalcitonin/lactate ratio were found in infected diabetic foot with osteomyelitis than those without osteomyelitis and those of diabetic foot ulcer without infection and those without foot complications. Also, there was significant increase in those without osteomyelitis than in those of diabetic foot ulcer without infection and those without foot complications. Elevated WBCs, T. cholesterol and serum triglyceride were independent predictors of elevated procalcitonin (PCT)/lactate ratio. Procalcitonin/lactate ratio at cut-off value of ≥ 0.31 could be a marker for early detection of infected diabetic foot ulcers without osteomyelitis with 95.9 % sensitivity and 92.4% specificity. Also, cut-off value of ≥ 2.3 could be a marker for early detection of osteomyelitis in infected diabetic foot ulcers patients with.85.6% sensitivity and 77.4% specificity Conclusion: Procalcitonin/ lactate ratio, which is easy faster and cheaper than MRI could be a good marker for early detection of osteomyelitis in infected diabetic foot ulcer patients with high sensitivity and specificity and a dependable sign for acute DFI.