ABSTRAK Penelitian bertujuan untuk mengetahui viabilitas spermatozoa cauda epididimis pada berbagai konsentrasi pengenceran menggunakan air kelapa muda dan kuning telur yang disimpan pada temperatur 3-5oC. Pengencer Tris 80% + 20% kuning telur digunakan sebagai kontrol (P1), selanjutnya perlakuan menggunakan pengencer air kelapa muda 90% + 10% kuning telur (P2), air kelapa muda 85% + 15% kuning telur (P3) dan air kelapa muda 80% + 20% kuning telur (P4). Viabilitas spermatozoa yang diamati setiap hari meliputi persentase motilitas dan persentase hidup sampai mencapai motilitas minimum 30%. Hasil penelitian menunjukkan persentase motilitas tertinggi pada hari ke-4 terdapat pada perlakuan P4 sebesar 31.8 %, berbeda nyata (P<0.05) dengan P3 sebesar 10.5 % dan P2 sebesar 2.5 % serta dengan P1 sebesar 4.2 %. Pada persentase hidup spermatozoa, perlakuan P4 juga menunjukan nilai 50.3 %, berbeda sangat nyata (P<0.05) dengan perlakuan P1, P2 serta P3 berturut-turut adalah 27.8 %, 26.4 %, dan 32.9 %. Kesimpulan dari penelitian menunjukkan bahwa pengenceran dengan perlakuan P4 (80% air kelapa dan 20% kuning telur) mampu mempertahankan viabilitas spermatozoa cauda epididimis kerbau rawa selama proses penyimpanan hingga empat hari di dalam refrigerator dengan suhu 3–5oC. Kata kunci : kerbau rawa, spermatozoa cauda epididymis, air kelapa muda ABSTRACT Young coconut water provides the physical and chemical needs of spermatozoa to sustain the fertility and viability of spermatozoa. However, it is unable to protect the spermatozoa at low temperature. An experiment was conducted using cauda epididymis collected from swamp buffalo under four treatments (coconut water extender 90% with 10% egg yolk (P2), coconut water extender 85% with 15% egg yolk (P3), coconut water extender 80% with 20% egg yolk (P4) and Tris extender 80% with 20% egg yolk as a control (P1)) to examine the viability of spermatozoa cauda epididymis on various concentrations of dilution using young coconut water and egg yolk stored at temperature of 3-5oC. Spermatozoa viability was observed daily included the percentage of motility and live percentage up to a minimum motility of 30%. On the fourth day, percentage of motility for P4 treatment (31.8%) was significantly (P<0.05) higher than P3 (10.5 %), P2 (2.5 %) and P1 (4.2%). Whereas the percentage of live of spermatozoa was 27.8%, 26.4%, 32.9% and 50.3% on P1, P2, P3, and P4 treatment respectively. Coconut water extender 80% with 20% egg yolk could be used for maintain the viability of cauda epididymis of kerbau rawa during storage process up to four days in refrigerator at temperature of 3-5oC. Keywords: swamp buffalo, cauda epididymis spermatozoa, young coconut water.