An effective stabilizing method for organic molecules is a bottleneck preventing their industrial application. For example, β-carotene has the following remarkable features; ultrafast optical response, third-order optical nonlinearity, and so on. However, it has not been used as photonic-devices because it easily degrades by oxidation and isomerization. We have succeeded in encapsulating β-carotene inside of single wall carbon nanotubes. The stability of β-carotene is highly improved by the encapsulation.