This is a case report of first branchial cleft cyst in 56 year old male patient, which was tentatively diagnosed as acute right submandibular abscess resulted from the periapical lesion of the lower right second molar. The results are as follows, 1. The accompanying ipsilateral inflammatory swelling resulted from the periapical lesion of lower right second molar tooth makes the diagnosis difficult. 2. The onset of this case was very late in comparison to the mean discovering age of branchial cleft cysts. 3. The plain radiography using contrast media is helpful for the diagnosis of cystic lesions within soft tissues. 4. This case in a first branchial cleft cyst(Type I) which occurs less than 1% of all branchial cleft anomalies.