This paper proposes a new class of distributed nonlinear controllers for leader-following formation control of unicycle robots without global position measurements. Nonlinear small-gain design methods are used to deal with the problem caused by the nonholonomic constraint of the unicycle robot and yield simple conditions for practical implementation. With the proposed distributed controllers, the formation control objective can be achieved without assuming any tree sensing structures. More interestingly, the distributed controller is robust to position measurement errors and the linear velocities of the robots can be restricted to specific bounded ranges. (C) 2012 Elsevier Ltd. All rights reserved.