Dynamic modeling and fuzzy control of a tiltrotor unmanned aerial vehicle are presented. In order to design a full-conversion flight controller for a tiltrotor unmanned aerial vehicle, the dynamic characteristics of a small tiltrotor unmanned aerial vehicle during helicopter-to-airplane conversion is investigated. A six-degree-of-freedom nonlinear equation of motion using powered wind tunnel test data is developed based on a Bell Model 301 tiltrotor research aircraft. The time-varying characteristics of the conversion maneuver, over which system dynamics change rapidly, are handled by a Takagi-Sugeno fuzzy control approach in both longitudinal and lateral axes. Simulation results indicate that a small tiltrotor unmanned aerial vehicle exhibits nacelle tilt during the backward conversion flight from airplane to helicopter mode.