Different types of functionalized thermoplastic polyphosphazenes such as poly(bis(furfuroxy)phosphazenes) (PBFP), poly(bis(1-adamantanemethylamine)phosphazenes) (PBAP) and poly(bis(cyanophenoxy)phosphazenes) (PBCP) were synthesized and further characterized to study their flame retardant properties. Structural characterizations were carried out by using GPC, FTIR, 1 H & 31 P NMR and wide angle XRD. Beside this, the solubility behaviour of these synthesized polyphosphazenes was checked in various protic and aprotic solvents. Thermal analysis and combustion properties of synthesized polyphosphazenes were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry, UL-94 (vertical burning test) and cone calorimetry. The Limiting Oxygen Index values of synthesized polyphosphazenes were also determined from their % char yield obtained in TGA. It was found that the LOI value was highest for PBCP and lowest for PBAP amongst all substituted polyphosphazenes. Further, all the polymeric samples showed high flame retardancy with UL-94 V-0 rating. The water uptake property of synthesized polyphosphazene polymers was also invested by measuring their water contact angles which showed that all the polymers were hydrophobic in nature with their water contact angles in the range of 137 o to 141 o . Copyright © VBRI Press.