This study was done to determine the impact of rice straw as a substrate for periphyton production and phytoplankton biodiversity in earthen fish ponds belongs to the world fish center. The ponds have the same area of Six 1000 m² and the depth of water 1m. The ponds cultured with mono six Nile tilapia fry in the rate of 3 fry/ m².  All ponds were fertilized with dry chicken manure in the rate of 15 kg/pond/week, and divided into two treatments, each of 3 replicates; the first treatment (T1), the substrate free control, while second treatment (T2) received 45 kg dry rice straw/pond. The samples were collected monthly from May to December 2017. The quantitative measurements for phytoplankton showed that total count of phytoplankton in water was higher in T1 than T2. The rice straw was effective for controlling growth of cyanophyceae compared to controls, and was capable for inhibiting the growth of Microcystis. Phormidium, Merismopediam, Gloeocapsa, Lyngbya and Chlorella, but Chrococcus, Synedra and Navicula sp. had improved growth in the presence of rice straw.Concerning periphyton the total count was (2103.68 x 10⁶ org. /m² as an average). And Chlorophyceae represent the dominant group with average (1577.07 x 10⁶ org. /m²). The biodiversity index of overall phytoplankton genera Taxa evenness were (1.95 and 0.51) respectively in T2 which indicates that there is a high biodiversity of algae compared to T1 (1.76 and 0.42). The results of this investigation indicated that rice straw could introduce an accessible practical and commercial method to increased phytoplankton biodiversity.