Ber (Ziziphus mauritiana Lam.) is an ancient and poor man’s fruit crop grown in semi arid and arid regions of India and other few countries. In India, Z. mauritiana trees are a host for the lac insects, Kerria Lacca, which are found on the leaves and make an orange-red resinous substance widely used to make varnish (Sajeewa SN et al. 2011). Disease specimens were collected throughout the year from different parts of University campus Kota, Rajasthan India, where the plant was seen and the associated pathogens were isolated following standard laboratory techniques. Detailed microscopic studies were carried out in laboratory. The causal organism found was powdery mildew incited by Oidium erysiphoides f. sp. ziziphi Yan & Wang (Microsphaera alphitoides f. sp. ziziphi Griffon & Maublanc). It is a major disease in Ber producing regions of India, causing great loss in productivity and quality of fruits (Jamadar MM, Balikai RA and Sataraddi AR 2009, Lim et al. August 2003). This fungi is obligate parasite that require living hosts in order to complete their life cycles, so they readily infect healthy, vigorous plants. Therefore the present study was conducted to understand the knowledge about the causal organism found in University Campus Kota Rajasthan India and to further develop efficient management strategies for control of this disease.