An optical fiber monitoring system monitors an inter-building optical fiber connecting a first building and a second building. The optical fiber monitoring system includes a first visualization panel provided in the first building and optically connected to an one end of the inter-building optical fiber, a second visualization panel provided in the second building and optically connected to an other end of the inter-building optical fiber, and a monitoring light source provided in the first building to input a monitoring light into the inter-building optical fiber. The first visualization panel includes a first photosensor that partially leaks the monitoring light inputted into the inter-building optical fiber from the monitoring light source and detects an amount of a leaked light. The second visualization panel includes a second photosensor that partially leaks a light from the inter-building optical fiber and detects amount of a leaked light.