Lost Mosque, 7th-century mosque ruins in Lalmonirhat Sadar Upazila, Bangladesh.

The Lost Mosque is a 7th-century structure in Lalmonirhat that stands as ruins near a main road. The remains show original pillars still standing among the ancient foundations that outline the building's original footprint.

The mosque was built in 69 AH (688–689 CE), according to an Arabic inscription found among the ruins. In early 1987, locals told journalists and researchers about the site, and over a hundred scholars and archaeologists came to study it. The inscription is now kept at the Tajhat Museum in Rangpur.

Local people call the site Harano Masjid, the Lost Mosque, and it has been renamed Sahaba-e-Keram Mosque. A 6×6×2-inch stone inscription found in the rubble reads "La-ilaha-illallahu Muhammadur Rasulullah, Hijri year 69" in Arabic and is now kept at the Tajhat Museum in Rangpur.

The ruins lie in Ramdas Mouza, Panchagram Union, about 1 km south of the Rangpur–Kurigram highway. From Lalmonirhat town, take local transport toward the highway and continue on the rural access track. The site is unroofed and surrounded by vegetation, so sturdy shoes and rain protection are useful.

Two of the original pillars still stand upright today among the other ruins, showing the strength of the ancient structure. These preserved columns make the building's original scale visible to anyone who walks through the site.