A new route has been developed for preparing polyaniline (PANI) layered double hydroxide (LDH) nanocomposites through in situ chemical oxidative polymerization of metanilic anions (m-NH 2 C 6 H 4 SO 3 -) intercalated in NiAl LDHs under a nitrogen atmosphere by using pre-intercalated nitrate as an oxidizing agent. The interlayer space of NiAl LDHs has been used as an original nanoreactor for the in situ polymerization of the intercalated monomer. The whole process involves the synthesis of the precursor LDH [Ni 2 Al (OH) 6 (NO 3 )· nH 2 O], the intercalation of the monomer metanilic anions into the LDH and its in situ polymerization between the layers by thermal treatment under a nitrogen atmosphere. The interlayer polymerization reaction was monitored by thermogravimetric analysis (TG), differential thermal analysis (DTA), mass spectrometry (MS), UV/Vis absorption spec-