Toward memristor scaling, it becomes increasingly challenging to maintain reliable switching as the interelectrode distance shrinks to smaller and smaller scale. In particular, the memristive active layers are usually fragile and prone to metal-integration-induced damage. To adapt an ultrathin active switching layer for low-voltage operation requires alternative damage-free metal-integration strategies. Here, by adopting a van der Waals (vdW) metal-integration approach, we construct memristors with vdW contact between metal electrode and ultrathin native oxide on 2D material SnSe. The mild vdW-integration process preserves the delicate SnO_x and enables reliable Ag/SnO_x/SnSe memristor with low operation voltage, high ON/OFF ratio >10³, and excellent endurance and retention properties. Furthermore, the memristors feature gate-tunable neuromorphic functions. By carrying out multiterminal measurements and elemental analyses, we reveal an electrochemical metallization and Ag filament formation switching mechanism. Our strategy defines a unique vdW-integration solution for fragile memristive materials.