阿特金森循环（英语：Atkinson cycle）是一种由詹姆士·阿特金森（James Atkinson）于1882年发明的内燃机形式。阿特金森循环发动机提高了效率，但降低了功率密度，其缺点是在低转速时效率低，扭力较差，现阶段用在某些混合动力车辆上。

理想的阿特金森循环包括以下几部份：

• 1-2 等熵或是可逆绝热压缩
• 2-3 等容加热（Qp）
• 3-4 等压加热（Qp'）
• 4-5 等熵膨胀
• 5-6 等容冷却（Qo）
• 6-1 等压冷却（Qo'）

The Atkinson cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density, or total power extracted per unit of displacement per rotation. A modern variation of this approach is used in some modern automobile engines. While originally seen exclusively in hybrid electric applications such as the Toyota Prius, some non-hybrid automobiles now feature engines that can run in the Atkinson-cycle as a part-time operating regime, giving good economy while running in Atkinson cycle, and conventional power density when running as a normal-cycle engine. Mazda Skyactiv models offering this capability include the Mazda 3 and MX-5.