The brain extracellular matrix (ECM) is involved in several aspects of neuronal development, plasticity, and pathophysiology. Chondroitin sulfate proteoglycans (CSPGs), consisting of core proteins with covalently attached chondroitin sulfate (CS) chains, are essential components of the brain ECM. During late postnatal development, CSPGs condense around parvalbumin-expressing inhibitory neurons (PV-cells) and form lattice-like ECM structures called perineuronal nets (PNNs). Enzymatic or genetic manipulation of PNNs reactivates neuronal plasticity in the adult brain, probably by resetting the excitatory/inhibitory balance in neural networks. Recent studies have indicated that PNNs control PV-cell function by enhancing the accumulation of specific proteins at the cell surface and/or acting as neuroprotective shields against oxidative stress. Since dysfunction of PV-cells and remodeling of CSPGs are commonly observed in several disorders, including schizophrenia, Costello syndrome, Alzheimer's disease, and epilepsy, modulation of PV-cell function by CSPGs may provide a novel strategy for these neuronal disorders. Here we review the potential roles of CSPGs as therapeutic targets for neuronal disorders, with particular focus on structural changes of CS chains under pathological conditions.