Antibacterial activity of organic and aqueous extracts of 15 Palestinian medicinal plants were carried against eight different species of bacteria: Bacillus subtilis, two Escherichia coli species, Staphylococcus aureus (methicillin resistant), two S. aureus (methicillin sensitive) species, Pseudomonas aeruginosa, and Enterococcus fecalis. Of the 15 plants tested, eight showed antibacterial activity. Each plant species has unique against different bacteria. The most active antibacterial plants against both gram-positive and gram-negative bacteria were Thymus vulgaris and Thymus origanium. The organic and aqueous extract from the same plants showed different activities; the organic extract showed the same or greater activity than the aqueous extract. Finally, the hole-plate diffusion method showed larger activity than the disc diffusion method.