The efficiency of an inductive power transfer (IPT) system rapidly decreases as the load power deviates from its rated value. Improvement of the efficiency at light loads is an important problem for IPT systems. In this study, an observer-based maximum efficiency point tracking (MEPT) controller for a series-series tuned IPT (SS-IPT) system is proposed. The proposed controller regulates the equivalent load resistance to the optimal regardless of the actual output power. To implement the MEPT controller, the optimal equivalent load for the maximum efficiency is identified for each output power. Furthermore, using voltage and current observers for the receiver (Rx) coil, the estimation of the equivalent load resistance is accomplished. Then, the MEPT controller regulates the load resistance using a feedback controller and the estimated equivalent load resistance. The proposed controller is a sensorless and communicationless controller because the Rx-side state parameters are estimated using the load observers and the current of the transmitter coil. A MEPT controller with a bandwidth of 5.5 Hz was constructed for an SS-IPT system. The transient responses and efficiency improvements were evaluated using simulation and experimental results. With the proposed controller, over 20% efficiency improvement was achieved under 10% output power condition.