The purpose of research that examines the influence of fermentation with cedar buffalo rumen contents differently to proximate component quality on rice straw, corn straw and rice straw-corn. The research was conducted in May and June 2012 in the Laboratory of Animal Feed Technology and Feed Science Laboratory, Department of Nutrition and Food Animals, Faculty of Animal Husbandry and Agriculture, Diponegoro University, Semarang. The material used in this study is the buffalo rumen contents, rice straw and corn straw. Research tools include: chopper, trays, plastic, scales, knives, pH meter, thermometer, label paper, tissue and apparatus for proximate analysis. Research using completely randomized design (CRD) 4x3 factorial with 3 replications. Factors that influence is the addition of cedar buffalo rumen contents and straw combination. Factors adding buffalo rumen contents, there are 4 levels of 0% (R0), 5% (R5), 10% (R10), 15% (R15) and R0 as the control is 0% waste fermentation. Another factor is a combination of rice straw and corn are 100% rice straw: 0% corn straw (P), 50% rice straw: 50% corn straw (PJ), 0% rice straw: 100% corn straw (J). Parameters measured were proximate component changes the dry matter, ash, crude protein, crude fiber, crude fat and extract materials without nitrogen. The data were statistically processed by analysis of the range and if there is a significant effect of treatment was continued multiple regions Duncan test at 5% level. Based on the results of the study showed an increase in dry matter, ash, crude protein and crude fat along with increasing cedar buffalo rumen contents. Levels best proximate components obtained at PJR10 straw