A memory module includes a plurality of memory units, an assembling holder and an engaging arrangement. The assembling holder includes an elongated unit housing having at least an elongated receiving slot extended therealong. The engaging arrangement includes a first assembling joint provided at a side edge portion of one of the memory substrates, and a second assembling joint provided at a corresponding side edge portion of an adjacent memory substrate, wherein the first assembling joint is fittedly and detachably engaged with the second assembling joint of the adjacent memory unit to alignedly couple the memory units with each other in an edge to edge manner to inset into the receiving slot of the elongated unit housing.