Nigde Alaaddin mosque, one of the early examples of the Classical Seljuk Architecture, was built in 1223 upon the orders of Abdullah bin Besera during the time of Alaaddin Keykubat. Its architects were Siddik bin Mhamut and his brother Gazi. Its portal, found on the east side and higher than the walls, is where the embellishments are most dense. It is filled in with geometrical motifs (semicircles, semi-stars, stars with eight points, etc.) leaving very little void. The portal has a seven-lined "mukarnas". The three-lined inscription on the niche bears information about who had the mosque built and when it was built. The two reliefs on either side of the inscription are considered to be women's heads or lion heads by researchers. The edges of the marble stones on the entrance door with a low arch are like that of a saw. Next to the minaret on the northeast corner is a smaller second portal.

The mosque has a rectangular, though close to a square, plan. The building is divided into three with two lines each of 4 piers. The celing of the middle nave, larger than the ones on the sides, is decorated with four lines of "mukarnas" and has an oculus. The ceiling in front of the mihrab has three domes. The dome to the west has squinches with "murarnases" of 8 lines. However, the dome to the east is placed on two pendentives and two squinches. The mihrab hnas 5 corners and "mukarnases". The borders on the sides are mainly decorated with geometrical motifs.

Alaaddin Mosque is one of the best examples of Seljuk mosques with its stonework, originality of its minaret, the great number of interior domes and its oculus.