The methanolic extracts of 19 Jordanian plants were combined with seven different antibiotics and applied to check the inhibitory effects of the combination on the resistance of Pseudomonas aeruginosa. A resistant strain of Ps. aeruginosa, which was isolated from a patient and a standard strain of the same microorganism were used in this study. Our results showed that there are significant variations in the effects of some combinations used on the resistant and the standard strains probably due to structural changes. Almost all the plant materials used in combination with penicillin G and erythromycin allowed full growth of the standard strain, while the combination with some plant materials like Gundelia tournefortii L. and Lepidium sativum L. inhibited the growth of the resistant strain. Chloramphenicol, gentamicin and cephalosporin can be given advantageously with almost all the plant materials used with few exceptions on the resistant strain. Nalidixic acid activity was improved significantly when combined with all plant materials and tested on standard strain. On the other hand, its activity on the resistant strain was slightly improved using the same combinations.