Biological control of weeds is the use of natural enemies to reduce the density to a tolerable level. The target of this is not removal but the reduction of the weed population to an economically low. Pseudomonas aeruginosa used here as bio control agent. In vitro, used as addition in two bioassay experiments on weeds compared to control. First experiment was using Pseudomonas broth culture. As results, there was significant reduction reached to (40–85%) in growth parameters (lengths, fresh & dry weights and germination %) ofweeds(Echinochloa crus galli, Phalaris minor, Beta vulgaris L and Pennisetum purpuremum schumach Gramineae). The second experiment was using Pseudomonas ethyl acetate crude extract (organic extract). There were reductions in weeds growth parameters reached to (55-100%). In vivo, using Pseudomonas organic extract compared to control, there were significant reductions of weeds growth parameters reached to (21-82%). There was no negative effect on Zea mays growth parameters. There found unclear interactions between weed roots and soil microbes. It caused reductions in weeds rhizosphere microbes' counts. After weeds removed and Maize cultivated in same pots, soil microbes' counts increased during a month of Maize life in soil. Pseudomonas organic extract was identified by HPLC-MS to: Quinoline and Quinoline derivatives (Quinic acid, Quinolone 2-heptyl-4- hydroxyquinolone-N-oxide, 3-Quinolinecarboxylic acid, 1-ethyl-1, 4-dihydro-7-methoxy-4-oxo- and Quinolinediol. We recommend use Pseudomonas aeruginosa to reduce weeds especially with Zea mays cultivation and add biofertilizers. Effect of weed roots on soil microorganisms is unclear and needs more future studies.