Isoxya mossamedensis is a species of spider in the family Araneidae. It is found in southern Africa and is commonly known as the Angola Isoxya box kite spider.
Isoxya mossamedensis is found in Angola and South Africa. In South Africa, the species has been recorded from Mpumalanga, Gauteng, and Western Cape.
The species has been sampled from Grassland and Nama Karoo biomes at altitudes ranging from 400 to 1,692 m above sea level.
The species makes orb-webs between vegetation. Spiders are found in the web during the day.
Isoxya mossamedensis is listed as Least Concern by the South African National Biodiversity Institute despite being rare. The species is protected in the Aardvark Nature Reserve.
The species was originally described by in 1962 from Angola. Male identification remains problematic, with the species being known primarily from female specimens.