ABSTRACT. Miyasaki M.Y.A., Vale W.G., Baía F.A.C., Minervino A.H.H., Ribeiro, H.F.L. & Miyasaki M.T.A. [Comparison between Tris, Lactose/Tris, Ringer- Lactate and Skim Milk as extenders to deep freezing buffalo semen.] Comparação entre o Tris, Lactose/Tris, Ringer-Lactato e Leite Desnatado como diluidores na criopreservação do sêmen bubalino. Revista Brasileira de Medicina Veterinária, 36(1):1-10, 2014. Instituto de Biodiversidade e Florestas, Universidade Federal do Oeste do Pará, Campus Tapajós, Rua Vera Paz, s/n, Santarém, PA 68035-110, Brasil. E-mail: firstname.lastname@example.org The objective of the present experiment was to test the effectiveness of different extenders, as TRIS (hydroxymethyl-amino-methil-methan), Lactose/ TRIS, Ringer-Lactate and Skim Milk, for deep freezing and cryopreservation of buffalo semen. Three male Murrah buffaloes were submitted to semen collection through artificial vagina, totaling 71 ejaculates. After collection, each sample was subjected to analysis of physical and morphological characteristics of semen. The ejaculates were fractionated, diluted and frozen in four diluents. After deep freezing process the frozen semen were thawed at 40°C for 30 seconds and sequentially evaluated for motility, vigor, acrosome damage, and percentage of sperm abnormalities. The thermo-resistance test (TCT) was used to evaluate the post-thawing of motility and sperm vigor characteristics at 3-5 minutes, 30 minutes, 1 hour, 2 hours and 3 hours of incubation. After thawing the spermatic vigor decreased significantly (p<0.05) in every four treatments, yet when compared, the Ringer-Lactate, Lactose/TRIS and Skim Milk, without any statistical difference with exception between Skim Milk and TRIS (p<0.05). Regarding sperm abnormalities, the major, minor and total sperm defects, after thawing, all treatments showed increased number of defects (p> 0.05), however no statistical differences were observed when compared with each other (p>0. 05). In the post-Thermo Resistance Test, after three hours of incubation, motility and sperm vigor showed no statistical difference between treatments (p<0.05). The sperm acrosome membrane integrity after thawing were decreased with statistical difference (p<0.05), however when comparing this parameter between treatments, there were no statistically significant differences (p> 0.05). Notwithstanding, the observed results allowed to be concluded that the four extenders used have demonstrated satisfactory function when used in deep freezing of buffalo semen, with adequate technical and economic feasibility for this biotechnology applied to animal species used.