Sensor localization has become an essential requirement for realistic applications over Wireless Sensor Networks (WSNs). Radio propagation irregularity and the stringent constraint on hardware cost, however, make localization in WSNs very challenging. Range-free localizations are more appealing for range-based ones, since it does not depend on received signal strength to estimate distance and thus needs simple and cheap hardware only. In this paper, we propose a ring-overlapping, range-free approach using Ring Overlapping based on Comparison of Received Signal Strength Indicator (ROCRSSI). Simulation results have verified the high estimation accuracy achieved with ROCRSSI.