在光学上，牛顿环（英语：Newton's rings），也叫做牛顿圈，是一个等厚薄膜干涉现象。将一块平凸透镜凸面朝下放在一块平面透镜上，将单色光直射向凸镜的平面，可以观察到一个个明暗相间的圆环条纹。若使用白光，则可以观察到彩虹状的圆环彩色条纹。第一个对此现象进行分析的人是英国物理学家艾萨克·牛顿爵士，因而命名为牛顿环。

牛顿环现象是由平凸透镜下凸面和平面透镜的上平面（即两透镜间的空气薄膜的上下表面）所分别反射的光线产生干涉的结果。光线进入平凸透镜到达凸面进入空气时，一部分在该界面发生反射，另一部分透射后在下方的平面透镜发生反射，并与前一束后一次反射是在空气（光疏介质）—玻璃（光密介质）界面上发生的，反射光发生半波损失而与入射光反相。

Newton's rings is a phenomenon in which an interference pattern is created by the reflection of light between two surfaces—a spherical surface and an adjacent touching flat surface. It is named for Isaac Newton, who first studied the effect in 1717. When viewed with monochromatic light, Newton's rings appear as a series of concentric, alternating bright and dark rings centered at the point of contact between the two surfaces. When viewed with white light, it forms a concentric ring pattern of rainbow colors, because the different wavelengths of light interfere at different thicknesses of the air layer between the surfaces.