Diarrheal diseases constitute one of the major causes of morbidity and mortality in infants and young children globally. One of the main microorganisms causing diarrheal diseases is Campylobacter jejuni. For treatment of these diseases, Portulaca oleracea has been widely used as a folk remedy for a long time. This study was performed to investigate the antimicrobial activity of P. oleracea against gastroenteritis pathogens including C. jejuni. P. oleracea was extracted with petroleum ether, chloroform, ethylacetate, methanol, and hot water. The antimicrobial activity of the P. oleracea extracts was determined using the paper disc method, minimum inhibitory concentration, and the liquid culture method. The 10 $mg/m{ell}$ ethylacetate extract showed the strongest antimicrobial activity against Salmonella typhimurium, Salmonella enteriditis, and Shigella spp.. The hot water extract from P. oleracea showed the highest anti-microbial activity against C. jejuni at 10~20 $mg/m{ell}$. The hot water extract of P. oleracea retarded the growth of C. jejuni for 36 hr at $42^{circ}C$.