紫外线指数(英语：Ultra-violet Index)指的是在某一天某个地点受到太阳紫外线(UV)辐射强度的国际计量标准。这种级数主要用于日常预报中且针对对象是一般大众。

它的目的是用来保护人们免受紫外线的伤害。皮肤过量暴露在紫外线中会导致晒伤，眼睛伤害例如白内障，肌肤老化增加皱纹和皮肤癌。公共卫生组织建议人们在紫外线指数大于或等于3级时要采取措施保护自己(例如，可以在皮肤上涂抹防晒霜和戴帽子)，具体措施详见下表。

The ultraviolet index or UV Index is an international standard measurement of the strength of sunburn-producing ultraviolet (UV) radiation at a particular place and time. The scale was developed by Canadian scientists in 1992, then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994. It is primarily used in daily forecasts aimed at the general public, and is increasingly available as an hourly forecast as well.