An assembly method of a laundry treating apparatus comprising: a first step of positioning a second treating apparatus in a desired place for assembly, the second treating apparatus including a second front panel forming a front surface, provided with an upper fastening unit bent from an upper surface and extended to an upper portion, a second rear panel forming a rear surface, a second side panel located at both sides of a side direction, and a second drum rotatably provided between the second front panel and the second rear panel, providing a space in which laundry is stored; a fifth step of attaching a guide panel onto the second treating apparatus after the first step is performed; a second step of seating a first treating apparatus on the second treating apparatus after the fifth step is performed, the first treating apparatus including a first front panel positioned in the same direction as that of the second front panel, forming a front surface, a first rear panel positioned in the same direction as that of the second rear panel, forming a rear surface, a first side panel positioned in the same direction as that of the second side panel and located at both sides of the side direction, and a first drum rotatably provided between the first front panel and the first rear panel, providing a space in which laundry is stored; a sixth step of detaching the guide panel from the second treating apparatus after the second step is performed; a third step of coupling the upper fastening unit with a lower portion of the first treating apparatus after the sixth step is performed; and a fourth step of coupling a control panel onto a panel seating portion provided between a lower surface of the first front panel and the upper surface of the second front panel after the third step is performed, wherein the upper fastening unit is positioned to be higher than the lower surface of the first treating apparatus. a first step of positioning a second treating apparatus in a desired place for assembly, the second treating apparatus including a second front panel forming a front surface, provided with an upper fastening unit bent from an upper surface and extended to an upper portion, a second rear panel forming a rear surface, a second side panel located at both sides of a side direction, and a second drum rotatably provided between the second front panel and the second rear panel, providing a space in which laundry is stored; a fifth step of attaching a guide panel onto the second treating apparatus after the first step is performed; a second step of seating a first treating apparatus on the second treating apparatus after the fifth step is performed, the first treating apparatus including a first front panel positioned in the same direction as that of the second front panel, forming a front surface, a first rear panel positioned in the same direction as that of the second rear panel, forming a rear surface, a first side panel positioned in the same direction as that of the second side panel and located at both sides of the side direction, and a first drum rotatably provided between the first front panel and the first rear panel, providing a space in which laundry is stored; a sixth step of detaching the guide panel from the second treating apparatus after the second step is performed; a third step of coupling the upper fastening unit with a lower portion of the first treating apparatus after the sixth step is performed; and a fourth step of coupling a control panel onto a panel seating portion provided between a lower surface of the first front panel and the upper surface of the second front panel after the third step is performed, wherein the upper fastening unit is positioned to be higher than the lower surface of the first treating apparatus.