Experiments were carried out to knowing the effect of cassava peels fermentation which different EM4levels on in vitro partial VFA concentrations and what is the best level of EM4 used in cassava peelfermentation to obtain optimal in vitro partial VFA concentrations. Experiment using technique withcoompletely randomized design, 4 treatmens 3 replications P0= 0% unfermented cassava peel, P1=cassava peel using Effective Microorganisme-4 5%, P2= cassava peel using Effective Microorganisme-410%, P3= cassava peel usinEffective Microorganisme-4 15%. The parameters studied were acetic,butyric and propionic acids. The data were analyzed using Mikrosoft Exell 2007. The concentration ofacetic acid varied between 62,38%-72,99%, the concentration of butyric acid varied between 3,09%-6,44% and the concentration of propionic acid varied between 5,04%-12,45%, further test data determinethat the fermented yam skin flour was not different take effeck in the partial VFA of acetic, butyric andpropionic acids (P<0,05). The conclusion was that cassava peel use EM4 at different levels determinedthat the partial VFA concentration.was relatyvely the same. Eksperimen dilaksanakan untuk mengetahui efek kulit ubi kayu pada level Effektif Mikroorganisme-4yang berbeda pada konsentrasi VFA parsial secara in vitro dan berapa level terbaik dari EM4 digunakandalam fermentasi kulit ubi kayu untuk mendapatkan konsentrasi VFA parsial in vitro optimal.Eksperimen menggunakan teknik Rancangan Acak Lengkap, 4 perlakuan 3 ulangan P0= kulit ubi kayutidak difermentasi 0%, P1= kulit ubi kayu menggunakan Efektif Mikroorganisme-4 5%, P2= kulit ubikayu menggunakan Efektif Mikroorganisme-4 10%, P3= kulit ubi kayu menggunakan EfektifMikroorganisme-4 15%. Parameter yang diteliti yaitu asam asetat, butirat serta propionat dapatdianalisis data menggunakan Microsoft exell 2007. Konsentrasi asam asetat bervariasi antara 62,38%-72,99%, konsentrasi asam butirat bervariasi antara 3,09%-6,44% serta konsentrasi asam propionatberagam antara 5,04%-12,45%, hasil analisis statistik menentukan tepung kulit ubi kayu difermentasipada taraf yang berbeda tidak berpengaruh nyata pada VFA Parsial asam asetat, butirat, serta propionat(P<0,05). Simpulan, fermentasi kulit ubi kayu menggunakan EM4 pada taraf berbeda menghasilkankonsentrasi VFA parsial relatif sama.