Karni Mata Fair is held twice a year at Deshnok, a small town near Nokha in Bikaner district. The first and larger fair is held in March-April during the Navratras from Chaitra Shukla Ekam to Chaitra Shukla Dashmi. The second fair is held in September-October, also during the Navratras, from Ashvin Shukla to Ashwin Shukla Dashmi.

Karni Mata was an ascetic who led a righteous life dedicated to the service and uplifting of the poor and downtrodden of all communities. It is believed that she possessed supernatural powers. The foundation of Deshnok was laid by her and she has been worshipped as a goddess by her principal followers, Charans, as well as the rulers of Bikaner, who regarded her as the patron deity. The Karni Mata Fair is held in her honour.

The Karni Mata temple at Deshnok is a stone and marble structure and is also known as Madh. Inside the shrine, a 75 cms. image of Kami Mata adorned with a mukut (tiara) and garlands is installed. Her image is accompanied by the images of her sisters and the sisters of Avad Mata. The Rajputs bring their children on Jadula (their first hair cut) and place them at the deity's feet for blessing. The temple is thrown open to the public early in the morning at 4.00 a.m. Charan priests perform Mangla-Ki-Aarti and offer bhog (special food) as worship.

A peculiar characteristic of the temple is the legion of brown cats roaming about in large numbers in the temple. They are considered auspicious and the devotees make offerings. Two kinds of offerings, the 'dwar-bhent' is attributed to the priests and the workers. The 'kalash-bhent' is utilised for the temple maintenance and development.