A lightweight modular bed includes a bed frame unit, a first retaining unit, a second retaining unit, a supporting web unit, a vibration motor, and a cover patch. The first and second retaining units are coupled to two lateral portions of the supporting web unit to permit a web body of the supporting web unit to be fully stretched. A peripheral margin of the cover patch is secured to a boundary of a predetermined mounting region of the web body to permit a motor body of the vibration motor to be disposed therebetween. When the web body is fully stretched, top and bottom surfaces of the motor body are brought into abutting engagement with the cover patch and the predetermined mounting region, respectively.