The purposes of this study were to determine the phytochemical constituents and in vitro antimicrobial efficacy of Aerva javanica (L.) leaf extracts growing wildly in Al-Baha region, Saudi Arabia.  The plant leaves were collected, air-dried, macerated, and then extracted with ethanol, chloroform and hot water. The phytochemical constituents and antimicrobial potential against Gram-positive bacteria including; Staphylococcus aureus, Bacillus cereus, Gram-negative bacteria such as; Escherichia coli, Pseudomonas aeruginosa, and the yeast fungus Candida albicans were determined. Results indicated that the extracts contained saponins; coumarins, alkaloids, tannins, flavonoids and steroids. Gas chromatography-mass spectrometry (GC/MS) analysis revealed the presence of 38 different compounds in the ethanol extract, 41 compounds in chloroform extract, and 27 compounds in the aqueous extract.  As the concentration of the ethanol extract increased from 25 mg/ ml to 300 mg/ ml, the in vitro antimicrobial potency against the tested microorganisms increased. At 50 mg/ ml, the extract was inactive recording an inhibition zone (IZ) diameter of 0-8 mm, partially active (9-11 mm IZ) at 100-200 mg, and active (11-15 mm IZ) at 300 mg/ ml.  At 25-100 mg/ ml, the chloroform extract expressed partial activity against all the tested microorganisms recording an IZ of 11-12 mm, active (13-15 mm IZ) against E. coli, P. aeruginosa, S. aureus, and B. cereus, and very active (20 mm IZ) against C. albicans at 300 mg/ ml. Finally, at 25-100 mg/ ml; the aqueous extract had no activity (0-8 mm IZ) against E. coli, P. aeruginosa, S. aureus, and B. cereus, but was partially active against all the tested microorganisms at 200-300 mg/ ml; recording IZ of 9-11 mm. Findings of this study revealed that A. javanica plant extracts could be used as potent antimicrobial agents against the harmful microorganisms in the food and pharmaceutical industries.