Layered double hydroxide (LDH) is an important layer-structured material for supercapacitors because of its versatile compositions, high theoretical capacitance, environmental friendliness, and low cost. However, the high resistivity of this material results in capacity fading, limiting its application in energy storage. Herein, we develop a facile approach to synthesize ultrathin petal-like NiAl layered double oxide/sulfide (LDO/LDS) composites with high electrochemical activity using a hydrothermal reaction followed by a sulfidation process. Scanning electron micrographs show that the petal-like NiAl LDO/LDS composites are as thin as ∼10 nm with a mean lateral dimension of ∼1 μm. The NiAl LDO/LDS electrode delivers a remarkably high specific capacitance of 2250.5 F g⁻¹ at 1 A g⁻¹ compared with that of NiAl LDH (1740.5 F g⁻¹ at 1 A g⁻¹) and possesses a good cycling stability of 88.9% capacitance retention over 5000 cycles at 5 A g⁻¹. An asymmetric supercapacitor (ASC) is fabricated using NiAl LDO/LDS and graphene as positive and negative electrodes, respectively. The NiAl LDO/LDS//G ASC exhibits a specific capacitance of 153.3 F g⁻¹ at 1 A g⁻¹, a high energy density of 47.9 W h kg⁻¹ at a power density of 750 W kg⁻¹, and a reliable cycling stability of 95.68% capacitance retention after 5000 cycles. The results highlight that NiAl LDO/LDS composites are promising materials for energy storage devices with long cycling stability.