In 1331, his plan to overthrow the Shogunate was again discovered because of the betrayal of his close associate, Sadafusa YOSHIDA. The Emperor sensed danger, and quickly decided to leave the imperial palace with the Three Sacred Treasures of Japan, raised an army and secluded himself in a castle in Mt. Kasagi in Kyoto (today's Kasagi Town, Soraku District, Kyoto Prefecture). The castle, however, fell to the attacks of the Shogun's army and he was arrested.
元弘元年（1331年）、再度の倒幕計画が側近吉田定房の密告により発覚し身辺に危険が迫ったため急遽動座を決断、三種の神器を持って御所を脱出した上で挙兵し笠置山(京都府)（現・京都府相楽郡笠置町内）に篭城するが、圧倒的な兵力を擁した幕府軍の前に落城して捕らえられる。