The 269sq km PWS is the smallest protected area in Bhutan. In 1974, PWS was established as Phibsoo Reserved Forest and in 1993 it was upgraded as wildlife sanctuary. The sanctuary's first conservation management plan was approved in 2012. Subsequently in 2014 PWS was separated from Sarpang Forest Division, becoming an independent office.

The elevation ranges from 200 meters to 1,600 meters above mean sea level. PWS stretches its border from right flank of Punatsangchhu (Sunkosh) River in the west till Singye village in the east and with Dhanishri ridge bordering the north edge. The entire southern boundary shares Indo-Bhutan International border with Ripu-Chirang Reserved Forest. PWS covers Nichula and Singye gewog under Dagana and Sarpang dzongkhag. The PWS headquarter is located at Shariphu under Singye gewog. The sanctuary has 94 households in Nichula and 13 households in Singye Gewog.
PWS falls in the Indo-Malayan bio-geographic realm. Entire area has sub-tropical forest ecosystem which can be categories into Sub-tropical Semi Evergreen Forest, Sub-tropical Moist Deciduous Forest and Subtropical Moist Evergreen. There are approximately 1259 acres of plantations created between 1960 and 1975. PWS has one of the richest biodiversity, despite being the smallest park in the country. It is home to all the eight (8) cat species, Asiatic elephant, guar and endangered golden langur. It is the only natural habitat of spotted deer (Chital) and wild sal and agar wood forest in the country. In the recent past PWS have proven to be the potential habitat of globally endangered White-bellied heron along Phibsoo river and Longa river. It has over 300 acres of pristine subtropical rangeland, which is potential prime habitat of pygmy hog and hispid hare. There are about 637 species of flowering plants, 28 species of mammals and 132 species of birds recorded still there are chances of increasing the numbers of flora and fauna over time.