Ceramic products produced depend not only on the over-all chemical composition but also on the individual compositions, its crystalline structures and particles sizes of the raw materials. It has also been revealed that the appropriateness of particle size of materials used and the crystalline formation is much desired in the production of high strength electrical porcelain insulator. There is virtually no study conducted locally in Nigeria reviewed by the author at the point of compiling this study gave credence to particle sizes of materials as a considerable factor in producing their porcelain insulator. However, the dielectric and mechanical properties of the electrical porcelain insulators produced still need to be improved upon in order to produce high strength electrical porcelain insulators. The study therefore experiments by varying particle sizes 75µm, 150µm, and 300µm at developing electrical porcelain insulator with quality mechanical and dielectric strength using locally sourced raw materials. The raw materials were mixed by adopting two varied formulations from previous study, while slip cast techniques was employed in producing test samples sintered at 1200oC at the rate of 5 oC per minute. The physio-mechanical properties and dielectric strength of the samples were carried out in accordance to American Standard for Testing and Materials (ASTM) C20-00, and ATSM D116 standards.  Sample A1S of 75 µm particle size is the most acceptable of all the sample that met the required physio-mechanical and dielectric strength properties. However, this study suggests that 150µm particle sizes as a starting powder for production of electrical porcelain Insulator could also be used since its cost of processing is not much unlike 75 µm particle size and could easily be achieved locally in Nigeria.