Both of them lie parallel to the Hazarduari Palace's south face on the banks of the Bhagirathi River.
The old one lies a little south to the new one and on the west of the clock tower and just beside the place where the Bacchawali Tope rests.
The old mosque constructed by Nawab Siraj ud-Daulah, and soil from Mecca was brought which was mixed with its foundation, so that it could provide an opportunity to the poorer members of the local Muslim community to have an experience of Hajj, one of the five pillars of Islam.
The old mosque is smaller compared to the one built by Nawab Nasur Alikhan and is single domed.
The new mosque is built on a raised platform decorated with ornamental china tiles, and the foundation contains soil from Karbala.