In the present work, phosphazene core-based polyimide and polyhedral oligomeric silsesquioxane (POSS)-reinforced phosphazene polyimide nanocomposites were developed and characterized. The molecular structure of cyclophosphazene amine (PZA) was confirmed by H-1, C-13 NMR and MASS spectroscopic methods. The developed polyimide and its composites were studied for optical, thermal and dielectric properties along with their morphological studies. Interestingly, it was found that the incorporation of 10wt% of POSS-reinforced PZI composites possesses an improved glass transition temperature (Tg), thermal stability, char yield and flame-retardant behavior than those of neat PZI matrix. The value of dielectric constant gets decreased with increasing the weight percentages of POSS reinforcement and thus 10wt% POSS-reinforced PZI composites possesses the lowest value of dielectric constant (k=2.1). Further, it also possesses the highest UV shielding behavior in UVA region, i.e., 93% with minimum weight loss even after exposing for 165h. The antibacterial activity of the neat PZI matrix and POSS/PZI composites were also studied. The data obtained from different studies that it is suggested that the 10wt% of POSS/PZI hybrid composite materials can be used in the form of coatings, sealants and matrices in aerospace as well as microelectronics applications.