In the recent years, Mini Unmanned Aerial Vehicle (UAV) has generated a lot of interest both in military and civilian applications. Contemporary innovations have seen the entry of Mini UAV into a wide range of hitherto fore unexplored domains. Advancement in computer systems, miniaturisation of electronics, artificial intelligence and composite materials is propelling the development of Mini UAV. Mini UAV is a class of UAV within the large family of unmanned systems categorised by a set of parameters. However, there are glaring inconsistencies and lack of uniformity in specifying the parameters which define a Mini UAV. The paper explores the factors which define a Mini UAV to establish itself as a distinct class. Based on the review of the recent literature and various manufacturer’s data of Mini UAVs, both fixed-wing and rotary-wing, categorisation of Mini UAV have been analysed considering functional requirements of operating altitude, endurance, operating range, maximum take-off weight and size.