Leaf spot of Indian jujube (Zizyphus mauritiana Lam.) caused by Mycosphaerella arachidis Deighton has been recorded during winter seasons of recent years (2019–2024) in Odisha, India. Occurrence of the disease was first noticed in the month of September till continued up to January. M. arachidis turned to be an emerging pathogen under change in climatic condition and every time increasing their potentiality to infect a new host. A significant number of Z. mauritiana showed leaf spot symptom with approximately 55–60% average disease incidence. Leaf spots characterized with oval, circular, irregular patches which showed sequential color changes from light brown to reddish brown to pale brown encircling purple margin and ultimately grayish patches. The present research article describes the identification of the causal organism M. arachidis, its characterization and increasing host index. Optimum temperature (20–25 °C) coupled with moderate humidity (75–80%) during the pre-winter season helps in disease progress. To the best of our knowledge and review of literature study led to the conclusion that this is the first report of leaf spot of Z. mauritiana caused by M. arachidis from India.