Modern food processing technology has resulted in the creations of a new processed purple sweet potato product, one of which is the purple sweet potato ice cream. Ice cream is a frozen food product that are usually consumed as a desert, with main ingredients such as fat, nonfat dry material or nonfat solids, sweeteners, stabilizers, and emulsifiers (CMC). This research was aimed to determine the optimal CMC emulsifier concentration in making sweet potato ice cream. The experimental design used was Completely Randomized Design with four treatments, namely A1 level (control), A2 (0.1% CMC), A3 (0.3% CMC), and A4 (0.5% CMC). The results of this study indicate CMC concentration of 0.5% resulting in ice cream with a good quality, total sugar of 28.1%, fat of 5.67%, protein of 5.51%, total solids of 37.51% and water content of 62.47%. Organoleptic test results showed that with the CMC concentrations of 0.5%, the panelists gave texture attribute values of 3.5 and the degree of preference of 3:28. The purple sweet potato ice cream with CMC concentration of 0.5 percent had a good quality because it fitted with ice cream quality terms according to the SII. Keywords: carboxymethyl cellulose, ice cream, purple sweet potato ABSTRAK Teknologi pengolahan pangan modern telah menghasilkan kreasi baru olahan ubi jalar ungu, salah satunya adalah es krim ubi jalar ungu. Es krim adalah produk pangan beku yang biasa dikonsumsi sebagai makanan selingan dengan bahan-bahan utama dalam pembuatannya seperti lemak, bahan kering tanpa lemak atau padatan bukan lemak, bahan pemanis, bahan penstabil, dan bahan pengemulsi. Penelitan ini bertujuan untuk mengetahui pengaruh konsentrasi bahan penstabil (CMC) terhadap es krim ubi jalar ungu. Rancangan yang digunakan adalah Rancangan Acak Lengkap dengan empat taraf perlakuan yaitu A1 (kontrol), A2 (CMC 0,1%), A3 (CMC 0,3%), dan A4 (CMC 0,5%). Hasil Penelitian ini menunjukan konsentrasi CMC 0,5% menghasilkan es krim dengan kualitas baik, total gula 28,1%, lemak 5,67%, protein 5,51%, total padatan 37,51% dan kadar air 62,47%, Hasil uji organoleptik menunjukan konsentrasi CMC 0,5% lebih disukai panelis dengan nilai atribut untuk tekstur 3,5, dan tingkat kesukaan 3,28, Es krim ubi jalar ungu dengan konsentrasi CMC 0,5% memiliki kualitas baik karena sesuai dengan syarat mutu es krim menurut SII. Kata kunci: carboximethyl cellulose, es krim, ubi jalar ungu