This research utilizes particle swarm optimization (PSO) to minimize the total active power losses in an IEEE 6-bus transmission system. The complexity of the problem lies in integrating Newton-Raphson load flow algorithm, which is used in computing power losses, with PSO algorithm, which is used to minimize these losses. The considered PSO control variables are: the reactive power output of generators, the tap ratios of transformers, and the reactive power output of shunt compensators. PSO was chosen as optimization method due to its popularity as a successful algorithm in solving non-smooth global optimization problems. The proposed PSO algorithm gave very satisfactory simulation results. Power losses were reduced by 13.9% for an initial set of PSO parameters. These parameters were thereafter varied in order to improve PSO performance by further minimizing the power losses. Effectively, we were able to obtain a set of parameters that resulted in a 19.31% reduction in power losses. These successful simulation results confirm the effectiveness of PSO in minimizing distribution networks power losses.