The Optimal Incorporation Distributed Generation (OIDG) problem can be treated as a single objective or multi-objective optimization problem. The advantage of the second option is to give a set of solutions in one run while optimizing more than one objective at the time. This paper aims to investigate the OIDG for single and multiple units in radial distribution systems using a Decomposition Based Multiobjective Evolutionary Algorithm. Seven case studies have been investigated considering three objectives which are active power losses minimization, voltage stability enhancement, and voltage profile improvement. All these case studies are tested on the 33-bus radial system.