Abstract: The Affilitted Second Hospital of Lanchou medical College Cansu Province Detection SIgA Of in gastric juice is affected by acidity.The higher acidity and activity pepsin are able to degrade or to digeste 1g.so is s1gA. As pH<3.0. hardly detected it.pH< 5.0 Ig content is gradually decreasing, but so longas above pH 5.0 content is steady existence,Owing to sensibility of RSID limtation can not accurally under pH 5.0 content.So that the ELISA(douole of antibody sandwich)was established in aur department,and used in detected SIgA of gastnic juic for diagnosis with gastric cancer.The article report patients with gastric cancer detected with ELISA, positive rate was 94.4%(positive 68cases among 72cases)but 59 cases were detected with RISD in same group cases,Positive rate was 82.0%The diagnost ic rate waspromoted That it have significant in statistics test(p<0.05).IF gastric juice pH 5.0 is taken out from stomach and with NaOH neutralized in on time We should detected with this method.Therefore partly false negative cases can de avoided.However other false positive cases increased have no significant in statistics(p>0.05)Addition to the variety suitable condition and affected factors of detected SIgA in gastric juice are disscused. Our measure of setted probleme in expriments were summaried and interpreted.