It is generally accepted that Muslims played an important role in the history of Ayutthaya Dynasty. Several studies have been carried out on this topic by using historical documents and materials. In this article, however, the author try to examine the historical development and the religious social changes of Muslim communities n Ayutthaya by identifying the existing Muslim communities through our field research of Ayutthaya in 1992. As the result of this field research, twenty four Muslim communities have been identified in Ayutthaya, and at present time among then1 twenty one Muslim communities still exist. The old Muslim communities which were established by Persian, Indian, and Cham Muslims in Ayutthaya period had been abandoned since 1767 when the inhabitants of Ayutthaya had fled away. However the Muslim communities in Ayutthaya revived in the period of Ratanakosin Dynasty when King Kama I and Rama III brought Malay Muslims as prisoners of war and slaves to the Central Thailand. Those Malay Muslim were especially arranged to settle in the old Muslim communities in Ayutthaya, and that caused mixture of Malay Muslin1 with the other ethnic h1uslim groups. At present time the majority of the Muslim in Ayutthaya are Malay Muslim. Beside them, there are few Persian, Pakistan, Indian, and Cham Muslim staying in Ayutthaya. On the other hand among the Muslim communities of Ayutthaya there are segregation of Muslim communities and survival or revival of the Sufism. In this article the author would like to introduce these phenomena of the Muslim continuities in Ayutthaya.