Novel flame retardant materials is developed based on amine-terminated poly (amidoamine) dendrimers (PAMAM) and citric acid (CA) as a cross-linker. In the present approach, a durable flame retardancy and thermal stability are achieved for cotton fabric. The treated cotton fabrics were characterized for structural and thermal analysis using Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The flame retardant behavior of the treated cotton fabrics was improved significantly as the limiting oxygen index (LOI) value increased over 25%. Investigating the flammability of the treated cotton fabrics by vertical flame test showed a remarkable decrease in burning speed around 0.16 mm/s. It is found that the raw cotton fabric burned completely and rapidly with almost no residue after burning, while the treated fabric with PAMAM dendrimers using the citric acid left more residue with char length of 2 mm. The obtained results showed that both the thermal stability and flame retardancy of cotton fabric have significantly enhanced through the modification by PAMAM dendrimer together with citric acid. The results confirmed the durability of flame retardant finishing on the cotton fabrics after repeated washing and rubbing cycles. Furthermore, the air permeability of treated fabric have also been assessed, and it showed that the modification of cotton fabric with PAMAM dendrimer had negligible effect as it decreased only about 0.33%.