The study on Ichthyofaunal diversity of Himalayan stream Namphuk, which is originated from Myanmar and flows through Rima-Putok and Kharsang of Changlang district of Arunachal Pradesh, North-eastern part of India was carried out from December 2015 to November 2016. A total of Four sampling station was covered for the study period. Altogether 48 fish species belonging to 13 families from 6 orders were recorded from the river. The Cypriniformes formed the largest group with a contribution of 4 families, 21 genera and 34 species. Of the recorded species, following IUCN conservation status, 40 (83.33%) species were found as least concern, 3 (6.25%) species as near threatened, 2 (4.16%) as vulnerable, 1 (2.08%) as endangered and 2 (4.16%) species as not evaluated. Various Diversity indices were evaluated using Primer software. The Shannon wiener species diversity index (H) found to be highest (3.484) at station 4 in post monsoon season and lowest (1.6115) at station 1 in monsoon, Simpson diversity index (1-λ) recorded highest (1.0) at station 1 in monsoon and lowest (0.9702) at station 2 in monsoon season. The value of Margalef's richness index (d) found to be highest (8.0846) at station 3 in post monsoon season and lowest (2.5447) in monsoon at station 1. Pielou's evenness index (J) was recorded maximum (0.9858) at station 3 in post monsoon and minimum (0.9770) at station 2 in pre-monsoon season. The diversity indices were evaluated by using Primer software.