Strategic Management Accounting (SMA), as a bridge between strategy, decision-making, and operational control, has the potential to enhance cost transparency, inter-departmental coordination, and supply chain optimization in large organizations. In state-owned enterprises (SOEs), due to the complexity of public supply chains, socio-political pressures, and accountability requirements, hidden costs (such as costs of misalignment, capacity waste, rework, procurement delays, and transaction costs) can systematically undermine performance. This research is designed at the doctoral level, employing a mixed-methods approach (qualitative-quantitative), to analyze the role of SMA in supply chain optimization and hidden cost management in state-owned enterprises. The quantitative section is based on a survey of 286 usable questionnaires (from a hypothetical population of 2,100 in state-owned enterprises and public institutions) using Structural Equation Modeling (SEM); the qualitative section includes content analysis and two rounds of the Delphi method involving 16 experts (financial managers, procurement officers, and professors of management accounting). Preliminary findings indicate that SMA dimensions (strategic costing, value chain analysis, balanced scorecard, and activity-based costing) have a positive and significant relationship with the reduction of hidden costs and supply chain optimization (hypothetical path coefficients between 0.32 and 0.47, p < 0.01). Furthermore, information integration and the maturity of management control systems play a significant mediating role in translating SMA into operational results (hypothetical indirect effect = 0.21, p < 0.05). In the qualitative section, eight categories of hidden costs (procurement inefficiencies, inventory waste, waiting/delay costs, process rework, inter-departmental misalignment, transaction costs, supply risks, and opportunity costs) were identified as focal points for SMA intervention. Key Finding: SMA in state-owned enterprises is most effective when aligned with information integration, management control systems, and data governance; otherwise, its impact remains limited to "internal reports without action."