Abstract <p>High-performance filtration reducers for saturated brine drilling fluids present a novel alternative for drilling anhydrite and mudstone formations, ensuring operational safety and cost efficiency. Conventional filtration reducers are often limited by poor biotoxicity, necessitating the development of environmentally friendly alternatives. In this study, a novel melamine resin-based filtration reducer (MHAN) has been synthesized, exhibiting exceptional thermal stability (up to 302°C). The addition of 3.0 wt % MHAN has reduced the filtration volume of a saturated brine bentonite-based drilling fluid from 162.2 to 8.2 mL and decreased the filter cake thickness from 3.2 to 0.8 mm demonstrating an excellent filtration control. After aging at 200°C, the saturated brine drilling fluid system containing 5.0 wt % MHAN with a density of 2.3 g/cm³ maintains stable rheology and filtration control performance. Notably, MHAN is sulfur-free and exhibits high environmental compatibility, with an LC₅₀ value of 78,500 mg/L. This eco-friendly melamine resin effectively controls filtration loss in saturated brine drilling fluids, supporting sustainable development of oil and gas resources.</p>