The number of dogs suspected to have allergic diseases, such as food allergies and canine atopic dermatitis, has been increasing annually. In this milieu, the variety of therapeutic diets for allergies described as grain-free, is increasing. However, during recent years, contamination with allergens that are not listed as raw materials of therapeutic diets has been pointed out. Human foods even with trace amounts of allergens may cause serious health problems, and it is mandatory by law to label allergens in foods. Various inspection methods have been established for this purpose. However, there is no standard for allergens in dog foods. In this study, we used the domestic tests for allergen contamination in human foods to evaluate therapeutic diets for dogs and investigated the actual situation. A quantitative analysis was performed with five therapeutic foods for dogs; their labels did not include wheat, eggs, or milk, as a raw materials. Of the five products, three products had wheat and one product had egg, and the allergens were found to be mixed at amounts exceeding the labeling standard in human food. Milk contamination was not observed. Overall, we confirmed contamination of therapeutic diets for dogs with, allergens not listed in the labels. To better understand allergies in dogs, it is necessary to discuss labeling of dog food allergens.