Treated effluent wastewater is considered an alternative water resource which can provide an important contribution for using it in different purposes, so, the wastewater quality is very important for knowing its suitability for different uses before discharging it into fresh water ecosystems. The wastewater quality index (WWQI) may be considered as a useful and effective tool to assess wastewater quality by indicating one value representing the overall characteristic of the wastewater. It could be used to indicate the suitability of wastewater for different uses in water quality management and decision making. The present study was conducted to evaluate the Al-Diwaniyah sewage treatment plant (STP) effluent quality based on wastewater quality index (WWQI) for disposal according to Iraqi limitations. Wastewater samples were collected from Al-Diwaniyah STP during 2012-2016 and tested for a comprehensive analysis of physical and chemical analysis. The parameters included Total suspended solids (TSS), Nitrate (NO3), Biological oxygen demand (BOD5), and Chemical oxygen demand (COD). The determination of the WWQI was done using the weighted arithmetic method. The results showed that the effluent BOD5, COD and TSS concentrations were not in the Iraqi standards for effluent disposal. The WWQI of this effluent classified its quality within ranged from poor to very poor according to Iraqi standards (IQS) and very poor to very polluted under the world health standards (WHO), that could cause environmental pollution in the receiving river. The permanent solution is through the proper operation using scientific methods and training the operational staff using technical methods and then future solution, advanced treatment in the plant, by completing both the solutions above will lead to upgrade the effluent quality to achieve the required water standards.