A multicenter study (NCT00449670) conducted across Taiwan, Singapore, Hong Kong and Thailand evaluated the safety and manufacturing consistency of four formulations of an AS03A-adjuvanted H5N1 vaccine in terms of immune response against the vaccine-homologous strain (A/Vietnam/1194/2004). This manuscript presents data from the Taiwanese population. Methods: A total of 400 individuals, aged 18–60 years, were randomized into six groups (2:2:2:2:1:1 ratio) to receive two doses (21 days apart) of one of the four adjuvanted formulations (H5N1-AS03A-groups) or one of the two nonadjuvanted formulations (H5N1-DIL-groups). Blood samples collected before vaccination (Day 0) and 21 days after each vaccine dose were analyzed using hemagglutination inhibition (HI) assay. Adverse events were recorded. Results: All four AS03A-adjuvanted formulations induced comparable immune responses against the A/Vietnam/1194/2004 strain; following the second dose, immune response in terms of HI antibodies was higher in the H5N1-AS03A-groups {seroprotection rate=91.6% [95% confidence interval (CI): 87.9–94.4]; geometric mean titer (GMT)=177.6 (95% CI: 153.2–206.0)} compared with the H5N1-DIL-groups [seroprotection rates=5.0% (95% CI: 1.4–12.3); GMT=6.3 (95% CI: 5.4–7.4)]. Immune response against the heterologous A/Indonesia/05/2005 strain was also stronger in the H5N1-AS03A-groups [seroprotection rate=45.6% (95% CI: 40.0–51.4); GMT=20.5 (95% CI: 17.8–23.7)] compared with the H5N1-DIL groups [seroprotection rate=0.0% (95% CI: 0.0–4.5); GMT=5.0 (95% CI: 5.0–5.0)]. The overall reactogenicity profile of the adjuvanted formulations was clinically acceptable. Conclusion: The AS03A-adjuvanted H5N1 influenza vaccine formulations induced stronger immune response against the vaccine-homologous and heterologous strains than the nonadjuvanted formulations. The AS03A-adjuvanted H5N1 vaccine demonstrated a good immunogenicity and an acceptable safety profile in the Taiwanese population.