Based on phase information, a novel image feature detector-symmetry phase congruency (SPC) is introduced. It is consistent with the characteristics of human visual systems. SPC is calculated based on log Gabor wavelet. It uses the phase information and is invariant to image illumination and contrast. SPC can detect the features in Mach bands and in sinusoidal grating. This cannot be done simply by looking for local maxima in intensity gradient or by looking for local energy maxima. Compared with phase congruency (PC), the advantages of SPC are demonstrated.