The causes of decline of house sparrow (Passer domesticus Linnaeus, 1758) in urban and suburban areas of Jammu Region, J & KAbstract : The house sparrow (Passer domesticus) belonging to the family Passeridae is the most widely distributed land bird in the world. In India, it is distributed all over upto 4000 m in the Himalayas. In the recent times, its population had declined drastically in Europe and other countries of world. ln India its number has also reported decreased in many cities of Andhra Pradesh, Kerala, West Bengal and coastal areas. In urban and suburban areas of Jammu, its population has been found to decrease drastically in the past 10 years. The study is carried from March 2009 to March 2013 to find out the cause of decline in these areas. The lack of nesting sites in the modern concrete houses and decrease in number of mud houses was found to be the main cause of decline. The lacking of spiny shrubs and trees less than 7 ft. height most preferred by House Sparrow as roosting sites, lack of animal diet in early stage of nestling diet and intense competition for nesting sites from birds like Common Myna, Red -rumped swallow etc. were other major causes of decline reported. Other probable causes reported are electromagnetic radiations from mobile towers, predation and lack of water sites.