A chromia-pillared clay has been prepared by ion exchange type intercalation reaction between the sodium ion in montmorillonite and the trimeric chromium oxyformate (TCF) ion, and by subsequent heat-treatment. The structural and thermal properties have been systematically studied by thermal analysis, powder XRD, IR spec-troscopy, and XAS. The gallery height of~6.8 $AA$ upon intercalation of the TCF ion suggests that the $Cr_3O$ plane is parallel to the aluminosilicate layers. Even though the basal spacing of TCF intercalated clay decreases slightly upon heating, the layer structure was retained up to $550^{circ}C$ as confirmed by XRD and TG/DTA. Ac-cording to the EXAFS spectroscopic analysis, it is identified that the (Cr-Cr) distance of 3.28 $AA$ between vertex-linked CrO6 octahedra in TCF splits into 2.64 $AA$, 2.98 $AA$, and 3.77 $AA$ due to the face-, edge-, and corner-shared CrO6 octahedra after heating at $400^{circ}C$, implying that a nano-sized chromium oxide phase was stabilized within the interlayer space of clay.