The objective of the experiment was to study the motility and viability of spermatozoa of fresh semen, and the quality of extended semen with different sperm concentration in Dimitropoulos-modified extender. Semen was collected using artificial vagina from three 4-8 year old stallions (different breed). Semen characteristics and quality was evaluated macro- and microscopically. For longevity evaluation, semen was stored at room and chilled temperature, and was evaluated for motility and viability every 3 h. Prior extension, semen was centrifugated at 3000 rpm for 20 minutes. The condensed sperm was re-suspended in Dimitropoulos (DV) supplemented with 50 mM fructose with the concentration of 200, 100 and 50 x 106 spz/mL. All samples were stored at room and chilled temperature, and was evaluated for motility and viability every 3 h and 12 h for room and chilled temperature. Results of the experiments indicated that fresh semen characteristics was fairly good. For longevity evaluation, semen with motility of 48.33 and 10.42% was observed at 3 h and 12 h after the onset of storage. The extended-semen with 50 x 106 spz/mL showed significantly higher in term of motility and viability (P<.05) than that with 200 x 106 spz/mL, but for that of 100 x 106 spz/mL. It is recommended that sperm concentration should be 50 x 106 spz/ml for a long period storage with reasonable good quality. Key words: Stallion, Semen, Sperm Concentration, Dimitropoulos