Purpose: To test the effects of sequential application of potassium oxalate gel/adhesive agent on in vitro dentin permeability. Materials and Methods: Full crown preparations were made in extracted human molars to expose deep coronal dentin. The roots and pulp were removed and the resulting crown segments were connected to a special device (Flodec) to permit the measurement of the permeability of the specimens before and after treatments. Minimum and maximum permeability were recorded after smear layer and phosphoric acid treatment. A new smear layer was created and the permeability measured after the crowns were bonded with Single Bond (3M ESPE), One-Up Bond F (Tokuyama), and AdheSE (Ivoclar Vivadent), either according to manufacturer's instructions or after treating the acid-etched dentin with a 3 wt% potassium oxalate gel. The results were expressed as a percentage of maximum permeability values. Impressions and epoxy resin replicas from the crown segments were produced for SEM examination. Results: None of the adhesives were able to eliminate the fluid flow through dentin. Two-way ANOVA revealed that the application of potassium oxalate prior to the bonding procedures was the most effective technique in reducing the dentin permeability (p < 0.05), regardless of the adhesive used. SEM micrographs showed that transudation of dentinal fluid could be identified on the surfaces of all replicas. Conclusion: The use of potassium oxalate gel was effective in reducing the permeability of bonded dentin.96505512