Joyangru, which is located in Woodo mountain in Chuncheon, Korea, was a gate tower of Monsogak. There are little historical records about Joyangru except of the 20th-century records. To study about Joyangru history, a dendrochronological analysis was conducted. We identified also the species of woods, We took 87 samples of wood elements for the species analysis and 13 samples for the dendrochronological analysis. We found 78 hard pines(Diploxylon), 4 Douglass-fir, 3 exotic hard pines(Pinus ponderosa type) and 1 Shorea sp.(Dipterocarpaceae). In the dendrochronological analysis, 2 floor flames were dated in 1887 (with complete sapwood) and 2 beams in 1884. We concluded that Joyangru was reconstructed just after 1888, most likely in 1890 together with Monsogak.