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The attitude control system of an unmanned aerial vehicle (UAV) is a multi-input multi-output, strongly coupled, nonlinear and uncertain system. This study proposes a new attitude control approach for an UAV using the variable structure control theory, with a particular focus on the parameter uncertainty and external disturbance. Firstly, the mathematical model of UAV's attitude motion is derived from the Newton-Euler formulation, including the kinematics and dynamics equations. Then, the attitude controller is designed by use of double loop scheme, the outer loop and the inner loop, which both track the command attitude angles and angular velocities. And a fuzzy system is used to solve the chattering problem. Finally, simulation results demonstrate that the proposed controller accomplished attitude tacking precisely in spite of parameter uncertainty and external disturbance.