The upstream nickel industry is a strategic sector playing a vital role in supporting the national industrial supply chain and Indonesia's natural resource downstreaming program. However, high raw material heterogeneity, fluctuating process parameters, and limitations in quality control systems lead to product quality variability, which impacts production efficiency, energy consumption, and process stability. This study aims to identify the key determinants influencing quality variability in upstream nickel production systems, analyze the relationships between these determinants using a Quality Engineering approach, and formulate a conceptual framework of quality variability to serve as a basis for developing a prevention-based quality control system. The study employs a descriptive-analytic approach using mixed methods, integrating quantitative and qualitative data gathered through observations, interviews, document reviews, and questionnaires. Analysis was conducted based on the 5M+1E framework, encompassing the factors of Man, Machine, Material, Method, Measurement, and Environment. The results indicate that the Material factor is the most dominant determinant influencing quality variability, with a mean score of 4.70 (94%), followed by Machine (4.20 or 84%), Man (4.00 or 80%), Method (3.90 or 78%), Measurement
(3.50 or 70%), and Environment (3.30 or 66%). The findings reveal that quality variability is systemic in nature, with all determinants interacting and influencing the quality of the final product. This research produces a conceptual framework of quality variability determinants that can serve as a foundation for developing adaptive quality systems and prevention-based quality control within the upstream nickel industry.