A ducted contra-rotating coaxial rotor system was designed and tested to assess its potential use as a micro aerial vehicle (MAV). Performance measurements (thrust and power) of the system in hover and forward flight were obtained. The influence of several design parameters (rotor spacing, duct inlet shape, position of rotors within the duct, and tip clearance) on performance was determined. Performance measurements of the unducted coaxial rotor, as well as the unducted/ducted single rotor configurations, were also obtained to give a performance baseline for the ducted coaxial rotor. The aerodynamic characteristics of the isolated duct were assessed from loads measurement and surface flow visualization. While the net system performance of operating the coaxial rotor within the confines of a duct was not always improved, the ducted coaxial rotor concept is still attractive for a MAV based on total attainable thrust for a given rotor size and other operational benefits.