Objectives: To analyze the expression of tenascin, fibronectin, collagens I and III, osteonectin, and bone morphogenetic protein 4 (BMP4) in the extracellular matrix of pulp tissue in primary teeth during physiologic root resorption. Method and Materials: Eighteen teeth were decalcified and equally distributed into 3 groups (group I, teeth with two-thirds root length; group II, teeth with one-third root length; and group III, teeth lacking the root). Results: Immunohistochemical analysis showed that all the proteins were expressed. Tenascin, collagen I, and osteonectin showed strong and broad reactivity in group I, with weaker and rare reactivity in groups II and III. The expression of fibronectin, collagen III, and BMP4 did not vary with root resorption phase. Conclusion: The expression of tenascin, collagen I, and osteonectin was reduced in the extracellular matrix and odontoblasts during root resorption. This fact may be related to the decreasing pulp response to damage and treatment during the progression of root resorption. Keywords: dentin matrix, endodontics, immunohistochemistry, primary teeth, pulp, proteins