Allergen is one of the most important factors in the pathogenesis of allergic inflammation.? It can not only sensitize and trigger allergic response but also can induce tolerance through allergen-specific immunotherapy (AIT). Although AIT has been introduced since 1911, and there are many modality of allergen-based specific AIT been developed since then. Despite rapid progress of the modality, the impact of allergic diseases remain tremendous. It is estimated that AIT is used in less than 10%.To improved the modality of AIT, the successful elements of AIT including efficacy, safety, convenience and reasonable-cost were reviewed and described. The allergen extract and its response have to be measurable and should include all allergenic components to make sure its effectiveness. For the safety and convenience reason, allergenicity of allergen extract would be better been reduced and could be administrated through non-injection route. Allergen should be reasonable-cost and affordable. If all factors have been taken into consideration, AIT will be more acceptable and allergen-induced tolerance by AIT can be achieved.