A modular cabinet assembly has at least a first sub-cabinet and a second sub-cabinet. Each sub-cabinet includes a back board having at least two separate back board pieces that are pivotably connected to each other, a left side board pivotably connected to one of the at least two back board pieces, and a right side board pivotably connected to another of the at least two back board pieces. At least one shelf board having opposite ends is removably connected to the left side board and the right side board of either the first sub-cabinet or the second sub-cabinet. A first end board is connected to either an upper end of the first sub-cabinet or a lower end of the second sub-cabinet. A first connector removably connects the left side boards of the first and second sub-cabinets, and a second connector removably connects the right side boards of the first and second sub-cabinets.