Abstract: A pen with dual extension/retraction cartridges includes two pen tubes where each of a first pen tube and a second pen tube has a pen tip portion and a pen end portion and a writing insertion plate disposed inside the pen tube near the pen tip portion; and a guiding tube disposed at the pen end portion of the first pen tube having an elastic plate disposed at one side and a positioning fastener disposed at one side of the elastic plate and two positioning rings disposed at the peripheral of the guiding tube, and a guiding slot disposed at the pen end portion of the second pen tube where the guiding slot is provided with a positioning hole passing through one side and a fastener disposed around the peripheral of the guiding slot so that the first pen tube and the second pen tube are combined with the guiding tube and guiding slot respectively; and at least two cartridges inserted onto the writing insertion plates of the first pen tube and the second pen tube respectively.