Hepatitis B virus has been a major concern to the world as it has been a killer infection for many years. It is an infection that has adverse effects on the human liver causing cirrhosis, and hepatocellular carcinoma. In many countries, many persons had been infected in the past with this deadly disease, and it resulted in many deaths. This has been so, due to the high cost and time required to undergo laboratory checks and consult a medical doctor. Not so many people could afford the medical bills required for early detection of the virus. The researchers seek to curb the challenge with the development of an Expert System for Medical Predictions of Hepatitis B. The software is meant to accurately predict if a patient has hepatitis B or not, the extent of the infection if any, and also suggest treatment. This is to enable for early detection and treatment of infected patients. This reduces the cost and time required to get treatment for hepatitis B. The methodology adopted for the analysis of this work is Object Oriented Analysis and Design (OOAD) and Unified Modeling Language (UML). The program is written using JavaScript alongside HTML5 (Hyper Text Markup Language), CSS (Cascading Style Sheets) and bootstrap framework. The database is implemented using MySQL and the program is implemented using PHP (Hypertext Preprocessor). From the results, the Expert system has accurately diagnosed if a patient has chronic or acute hepatitis B and also prescribed suitable treatment.