Urea, one of the most important nitrogen fertilizers in the world, is usually combined with aldehydes to produce more stable resin fertilizers with controlled release behavior. Urea reacts with furfural to produce difurfurylidenetriurea in a heterogeneous phase at temperatures below the urea melting temperature. We performed a detailed kinetic study of the condensation reaction between urea and furfural in heterogeneous conditions by combining isothermal and non-isothermal differential scanning calorimetric (DSC) experiments. DSC results showed that this reaction occurs with the superposition of two unresolved processes: condensation reaction and urea melting. The evaluation of these complex experimental data allowed us to estimate the activation energy and reaction heat, and to achieve a complete picture of the reaction process occurring at the interface of urea particles. Finally, ab-initio calculations were carried out to support the experimental observations.