Chikungunya virus (CHIKV), an alphavirus endemic to tropical regions of Africa, Asia, and the Americas, causes a self-limiting febrile illness characterized by fever, headache, arthralgia, and rash. No specific antiviral treatment is currently available for CHIKV infection. AG129 mice, deficient in interferon α, β, and γ receptors, serve as a model to study viral pathogenesis and antiviral efficacy. This study evaluated infection outcomes in AG129 mice inoculated intraperitoneally with 10, 100, or 1000 plaque-forming units (PFU)/mL of CHIKV to identify the optimal viral dose for antiviral assays. Two mice per group were euthanized daily for seven days post-infection to collect serum, spleen, liver, kidney, and lower leg muscle for viral RNA quantification. Survival rates were 80% for mice infected with 10 PFU/mL and 0% for those infected with 100 or 1000 PFU/mL. Viral RNA was detected from day 2 post-infection in serum, spleen, kidney, and muscle in the 100 and 1000 PFU/mL groups, while RNA was detectable from days 3 to 6 in all tissues of the 10 PFU/mL group. These results support the use of 10 and 100 PFU/mL CHIKV to infect AG129 mice as models of mild and severe disease, respectively, for antiviral studies.