Polyaniline/eggshell powder composites are proposed as a novel ammonia detecting sensor. The conductive composite is prepared by mixing eggshell powder and polyaniline using polymerisation process, blended in an appropriate solvent. The mixture is deposited on an interdigit electrode. The solvent then evaporates leaving a polyaniline/eggshell powder composite film. The SEM micrograph shows better interfacial adhesion between the eggshell powders with polyaniline. The polyaniline/eggshell powder composite was assumed to process a face centred cubic (FCC) structure. The sensor S-2 with 0.5 g eggshell powder showed better ammonia gas response and selectivity than sensor S-0 without eggshell powder.