Aim: the purpose of this study was to evaluate the effect of four chelating agents on the structure of dentin of extracted teeth: Smear Clear (Sybron Endo), Largal Ultra (Septodont), Tubuliclean (OGNA Laboratori Farmaceutici), EDTA: 17% (OGNA Laboratori Farmaceutici). Methodology: slices of bovine teeth were dried in a Virtis Automatic Free- ze-Dryer for 5 days, weighed (Mettler AE 163 Dual Range Balance) and randomly distributed in nine groups. The speciments were subsequently exposed to the chelating agents for 3 or 9 min. Then the speciments were washed with distilled water, dried for 5 days and weighed again. Difference between pre- and post-operative weight were recorded. Results were statistically analysed using the Kruskal-Wallis test, the Mann-Whitney test as post-hoc test with P < 0.05. Results: loss of weight increased significantly with increasing time of contact of the chelating agents with dentine. There were significant difference between the four chelating agents for loss of weight. Largal Ultra chelating ability was significantly better than EDTA 17% followed by Tubuliclean and Smear Clear. Conclusions: under the circumstances of this in vitro study, there were significant differences between the four chelating agents for loss of weight. The EDTA concentration, only in part, influences the chelating activity. The extent of demineralization is related to the time of exposure to these solutions.