The old name of Sumangala Vihara is Yangal Vihara. In local tongue it is also called Yanga Baha. Sramanera Pragyarasmi and Sumangala changed the term yangal into Ya Mangal. So, its name transformed into "Yan Mangala Vihara." Bhikshu Sangha got this Vihara as the name of "Yan Mangala Vihara." Narada Mahasthavira from Sri Lanka had come in this Vihara. He advised to omit the term 'Ya’ and instead of it, he suggested to add 'Su.‘ So the term 'Yan Mangala‘ transformed into 'Sumangala‘ that means good. Thus, its name came into Sumangala Vihara. It is also called Sri Sumangala Vihara.

There are fifteen Mahaviharas in Patan. That means fifteen main Viharas. Sumangala Vihara is one of the branches (Kacha Baha) of Rudravana Mahavihara of Patan. Initially, it was the place of abode of both Theravada and Mahayana. It was donated to Bhikshu Sangha after the revival of Theravada Buddhism in Nepal. In that time whole building was damaged except main shrine. Later, it was renovated by Bhikshu Sangha. 

There is debate about the age of this vihara how many years is old. According to Hemraj Shakya, one of the famous scholars of Lalitpur has pointed that this vihara established eight hundred years ago. He claimed on the basis of mentioned in inscriptions while he was doing research of Rudravarna Mahavihara. He has found inscriptions. "Yanga Vihara Nivasi Mahimari" has written in inscription at full moon day of 272 N.S. Similarly, "Yanga Viharas Chawmha Sri Rajal Sraman has been mentioned on the inscription found in 306 N.S. In that time, Sramner Rajal had stayed in this Vihara. So he
pointed out in his book 'Shivadeva Sanskarit, Rudravarna vihara Chhagu Addyan' that this vihara has established 844 years ago.

The vihara was as private vihara. It was donated in 1943 by Shakya Family, father: Harshaman and mother: Motilani Shakya and their sons: Tej Bahadur, Harsha Bahadur and Dan Bahadur Shaky to Bhikshu Sangha. It was registered in 1950 under Bhikshu Sangha. The donate plate was accepted by Bhikshu Pragyananda, Shakyananda, Amritananda, amd Pragyarasmi.

Sumangala Vihara as Kacha Baha Sumangala Vihara is a Kacha Baha of Rurdravarna Mahaviahara. Before to understand the Kacha Baha, first, it needs to understand ―what is Vihara? The term Vihara comes from Sanskrit word 'Viharati’, which means to walk or to sit, thus to walk peacefully.7 In fact Viharas were originally built to accommodate monks and nuns and facilitate their religious practices. Therefore, a Vihara is a secluded place where the members of the sangha, those who renounce worldly desires, live together and practice the Dharma. Gutam Buddha also permitted his followers to live in abodes such as Vihara, Addhyaoga etc. In fact, Viharas were built protect the monastic from rain and accommodate them to continue practice during the rainy season.

In local tongue (Newari Language), a Vihara is called Baha or Bahi.  The term Baha is corrupted form the term Sanskrit term Vihara which denotes a Buddhist monastery. Most of the Baha are orgainzed in such way that Mu baha are affliated with Kacha Baha and Nani.8 Kacha Baha is the branch of the main Vihara. Nani is the attributed the resindential areas of Sangha Members. The Baha are little different from each other due to physical features, the pattern of rituals, the organizaton of the Sangha, its functions. There are many Buddhist viharas, popularly known as Baha or bahi in the Kathmandu valley. Most of these of Vihras are ancient; some of them are more than two years old. Those viharas were established by various individuals during different historical period.