Onion (Allium cepa L.) is one of the most important commercial vegetable crops grown in India. Inviewofthedestructivenature of purple blotch of onion the present investigation was conducted in different district of Biharduring Kharif and Rabi2018-2019.The highest disease incidence (37.17%) and intensity (38.95 %) was noticed in field of Pariaunna village of Nalanda district during Rabi season whereas highest disease incidence (21.24%) was recorded in field of village Kushahar and highest intensity (28.30 %) wasnoticedin field of village Paharpur district Vaishali during kharif season. While,thelowestdiseaseincidence(17.62 % )and (21.25%) intensity was recorded in Azampur village of Vaishali district during rabi season, but in kharif season lowest (8.74%) disease incidence and (10.85%) intensity was observed in village Basaria district Samatipur . Among the districts, severity of disease more in Nalanda (36.64%) and less in Vaishali (26.78%) were recorded duringrabi season, while less disease intensity (14.41%) in Samastipur district recorded in kharif season with highest value 26.21 % in Begusarai district.