Abstract: An adjustable double-decker rack including an upper shelf having a pair of fixing members, a pair of brackets each having a body portion engageable with the fixing members, a plurality of plugs each having a conical portion at one end and a collet portion at another end, a plurality of tubular members each connected at both ends with the conical portion of one of the plugs, and a tray adapted to dispose on the tubular members, and a lower shelf having a pair of movable frames each engaged with a lower portion of a corresponding one of the brackets and having a plurality of holes, a pair of main supporting rods each having an end engaged with the female connector of each of the movable frames, a plurality of plugs each having a conical portion at one end and a collet portion at another end, and a plurality of tubular members each connected at both ends with the conical portion of one of the plugs, whereby the lower shelf can be pulled out of the upper shelf in order to increase the capacity of the rack as requ