Background & Aims: Chronic pulmonary infection in patients with cystic fibrosis is predominantly due to infection by mucoid strains of Pseudomonas aeruginosa. Mucoid P. aeruginosa is due to the production of exopolysaccharide called also alginate. Alginate in addition to interference with the clearance of lung has antiphagocytic property. Optimal killing activity of P. aeruginosa requires opsonic antibodies. Since immunomodulatory effects of garlic on enhancing phagocytic activity has been proved, in this study the effect of combination of alginate and an immunomodulator protein of garlic on production of opsonic antibodies against P. aeruginosa mucoid exopolysaccharide has been investigated. Methods: Alginate was extracted from a 72-hour culture of P. aeruginosa strain 8821M and then DNase1, RNaseA and Proteinase k were added. Subsequently, alginate was purified with gel filtration chromatography by sephacryl S-400. Female BALB/c mice aged 6-8 weeks were divided into five groups and injected subcutaneously on days 0,7,14 with either alginate, garlic, alginate- garlic, R10 or alginate-R10 and opsonophagocytic killing activity was calculated in each group. Results: The purified alginate contained 34.6µg/ml uronic acid, 0.5 µg/ml nucleic acid, 1.45 µg/ml protein and 0.08µg/ml LPS. Opsonophagocytic killing activity after immunization with R10, alginate and their combination showed significant increases of respectively 69%, 67% and 82% comparing to the control group. Conclusion: Combination of P.aeruginosa alginate and immunomodulator fraction of garlic enhances immunogenicity to P.aeroginosa by the elicitation of opsonic antibodies in BALB/c mice.