The invention relates to an image sensor and a manufacturing method thereof. The manufacturing method of the image sensor is characterized by comprising the steps that a substrate on which multiple radiation sensing elements are formed is provided; first separating parts are formed on the substrate; and multiple color filters are formed between the first separating parts and correspondingly arranged above multiple radiation sensing elements, and the first separating plates are used for preventing the crosstalk of the radiation between multiple color filters, wherein formation of the first separating parts comprises the steps that dielectric parts are formed on the substrate; and a first metal layer is formed on the side wall of the dielectric parts.