A flame retardant with enhanced phosphorus-nitrogen content, 3,9-dipyrolidino-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide (DTDP) was synthesized by the reaction of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane (SPDPC) with pyrrole. The structure and the thermal stability of the compound were characterized by infrared spectroscopy (IR), nuclear magnetic resonance (H-1 NMR and C-13 NMR), mass spectroscopy (MS), elemental analysis, and thermogravimetric analysis (TGA). Using a static analytical method, the solubilities of DTDP in N,N-dimethylformamide (DMF) in the temperature range from 302.80 to 362.05K and in water in the temperature range from 303.65 to 360.75K were determined. The solubilities of DTDP in ethanol, acetonitrile, acetone, acetic ester, and DMF+water binary mixtures were also measured for comparison. The solubility data were correlated with an empirical equation.