Proper formation of neuronal dendritic branching is crucial for correct brain function. The number and distribution of receptive synaptic contacts are defined by the size and shape of dendritic arbors. Our previous research found that protocadherin 11 X-linked protein (Pcdh11x) is predominantly expressed in neurons and has an influence on dendritic branching. In this study, gain-of-function and loss-of-function experiments revealed that Pcdh11x acts as a negative regulator of dendritic branching in cultured cortical neurons derived from embryonic day 16 mice. Overexpression of wild-type Pcdh11x (Pcdh11x-GFP) reduced dendritic complexity, whereas knockdown of Pcdh11x increased dendritic branching. It was further demonstrated that Pcdh11x activates PI3K/AKT signaling to negatively regulate dendritic branching.