Circular winding brushless dc (CWBLdc) motor is a novel square-wave multiphase permanent magnet motor with high torque density and excellent vibration performance. It has good prospect in high power and performance applications. However, the control of CWBLdc motor depends on a precise rotor position. Consequently, its application is restricted in some situations where it is difficult to install position sensors. In view of the fact that the existing sensorless control methods are not suitable for the novel CWBLdc motor, a sensorless control algorithm based on the phase voltages and dc current detection is proposed to obtain a continuous and precise rotor position. The fundamental harmonic amplitude of the phase current is estimated based on the dc current, which eliminates the process of phase currents detection and reduces the complexity of the circuit. The error of the algorithm is derived in detail and its accuracy is analyzed theoretically in the paper. The experimental results show that the performance of the proposed sensorless control algorithm is equivalent to that of control with position sensor.