Biopolymer, a natural biodegradable polymer has attracted much attention in recent years. Global envirot mental awareness and fossil fuel depletion urged researchers to work in the biopolymer field. Some of tt biopolymers used for the fabrication of rechargeable batteries are cellulose, chitosan, pectin, agar-agar an carrageenan. An alternative energy storage system and also equivalent to lithium ion battery technology is also need today due to the environmental impact and safety limitations concerning lithium materials. To fulfill a these needs, in the present work, magnesium ion conducting polymer electrolyte for battery applications lc synthesized using Iota carrageenan and magnesium nitrate salt. One-gram Iota Carrageenan is complexed wit various concentrations of magnesium nitrate salt by solution casting technique. XRD technique confirms tf amorphous nature of film. FTIR confirms the complex formation between polymer and salt. DSC study wt carried out to analyze the glass transition temperature. AC impedance spectroscopy was used to study tf conductivity and dielectric properties of polymer electrolyte. One-gram I-Carrageenan with 0.4 wt% of (NO3)(2) has shown a maximum ionic conductivity of 6.1 x 10(-4)S/cm and it possess lowest activation energ value of 0.175 eV. A Primary battery was constructed using maximum conducting polymer electrolyte and i performance was studied.