This study employed transcranial direct current stimulation (tDCS) to examine whether the left posterior parietal cortex (LPPC) is causally involved in episodic memory retrieval. Thirty-six participants were assigned to the anodal or the cathodal stimulation group with the block-randomization method and engaged in three source memory tests on three separate days. During the test phase, the participants received anodal or cathodal stimulation over the LPPC scalp region in one visit, sham over the LPPC in another visit, and anodal or cathodal stimulation over the right primary motor cortex (M1) scalp region in the other visit. The results showed that source memory accuracy, but not old/new recognition performance, decreased significantly when participants in the cathodal group received stimulation over the LPPC scalp region in comparison to the other two stimulation conditions. No such effect was found in the anodal group. These findings provide evidence for the causal relationship between the LPPC and episodic memory retrieval.