Abstract: Background: Palm leaf is a by-product of palm plantations that can be used as a feed alternative. Ammoniation is a potential approach to increase the digestibility of palm by-products. Objective: This study aimed to determine the cassava leaf meal supplementation level as a source of branched chain amino acids for ammoniated palm leaf enriched with sulphur (S) and phosphorus (P) minerals as feed for cattle as examined in vitro . Materials and Methods: Samples of S and P mineral-enriched ammoniated palm leaf supplemented with cassava leaf meal were analyzed for proximate composition. In this study, ammoniated palm leaf samples enriched with S (0.40%) and P (0.27%) were treated with several cassava leaf meal supplementation levels. This study used a randomized block design with 6 treatments and 4 replications. The treatments tested were 6 levels of cassava leaf meal (0, 5, 10, 15, 20 and 25% dry matter). Dry matter, organic matter, crude protein, Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF), cellulose, hemicellulose and rumen fluid characteristics (pH, VFA concentration and NH3-N level) were evaluated. Results: The results showed that mineral (0.4% S and 0.27% P) and cassava leaf meal (5% of dry matter) supplementation exhibited higher digestibility compared to other treatments. This supplementation formula resulted in the following in vitro digestibility characteristics: dry matter (55.56%), organic matter (59.83%), crude protein (55.34%), NDF (56.99%), ADF (50.01%), cellulose (60.78%) and hemicellulose (71.35%). The rumen fluid characteristics of this formula were as follows: pH (6.70), VFA (129.89 mM) and NH3-N (15.84 g/100 mL). Conclusion: Sulphur and P mineral-enriched ammoniated palm leaf supplemented with cassava leaf meal had significantly increased digestibility and rumen fluid qualities. Treatment with 5% cassava leaf meal produced the highest digestibility and rumen fluid characteristics.