Oligodeoxynucleotides containing unmethylated CpG motifs (CpG oligos) have been shown to prevent development of allergic airway inflammation and airway hyperresponsiveness (AHR) in mouse models of asthma. Recently, we reported immunomodulatory oligonucleotides (IMOs) containing novel structures (immunomers) and synthetic immunostimulatory CpR (R=2'-deoxy-7-deazguanosine) motifs show potent stimulatory activity with distinct cytokine secretion profiles. Since type 2 T cells predominate in asthma and increase in type 1 cells can prevent the differentiation of naïve T lymphocytes to a type 2 phenotype, we hypothesized that IMOs can prevent the development of allergic airway inflammation and AHR in the ovalbumin (OVA)-sensitized and challenged mouse model. We found that co-administration of novel IMOs during OVA-sensitization abrogated both early and late allergic responses (LARs). AHR to methacholine was also blocked with IMO treatment. Analysis of bronchoalveolar lavage (BAL) fluid of mice treated with IMOs demonstrated complete reduction in eosinophils, with concomitant decreases in both serum and BAL fluid IL-4, IL-5, and IL-6 levels. In addition, there was a significant reduction in serum IL-10 levels. IMOs, in general, significantly attenuated the rise in serum IgE levels. In comparison, IMOs showed a significantly more potent effect on early and late allergic response than a conventional CpG oligo in this model. These data suggest that the treatment with these novel IMOs prevents OVA-induced allergic airway inflammation and AHR in asthma in the mouse and may provide a useful agent in the treatment of human asthma.