In this study, the alcoholic and lyophilized aqueous extracts from twenty wild medicinal plants belonging to two families from the Qassim area were studied. The sensitivity of eighteen microbes (five Gram-positive and six gram-negative bacteria, five fungi and two yeasts) to the prepared extracts at concentrations of 10, 25, 50, 100 and 200 mg/ml was investigated. The minimum inhibitory concentrations (MIC) for different active extract were also investigated against the tested bacteria. Alcoholic and aqueous extracts of the stuided plants exhibited a strong antibacterial activity against Staph. aureus, Staph. aureus (methicillin resistant), Strept. types B and D, Sali. type C, E. coli, H influenza Pr. mirabilis and Ps. aeruginosa. The values of MIC for C. bruguierana, R. stricta, P. harmala, C. coccineum (No. 6) and W. Somuiifera extracts against H. influenza were 8.36, 8.42, 8.47, 23.77 and 23.87 mg/ml, respectively. It has been also cbserved that fungi and yeasts were less sensitive, with the exception of T. mentagrophytes which was slightly sensitive to some plant extracts.