Objective To study the clinical discrepancy between patients with post infectious irritable bowel syndrome(PI-IBS) and non post infectious irritable bowel syndrome(NPI-IBS),and assess the value of serum intestinal fatty acid binding protein (I-FABP) for differential diagnosis.Methods A total of 117 patients with PI-IBS,201 patients with NPI-IBS and 31 healthy controls were prospectively recruited in General Liberation Army Hospital from 2010 to 2013.Plasma samples and clinical data were collected.Serum I-FABP level was measured by an enzyme-linked immunosorbent assay.Results The median age of patients with PI-IBS was 36 years.The median time to diagnosis in PI-IBS group was significantly longer than that in NPI-IBS group [(19.7 ± 10.3) months vs (11.4 ± 5.3) months,P ＜ 0.05].Similarly,the proportion of anxiety [58.1％ (68/117) vs 28.9％ (58/201),P ＜ 0.05] and the value of I-FABP[(42.6 ± 14.8) μg/L vs (17.3 ± 11.5) μg/L,P ＜ 0.05] in PI-IBS group were significant higher than NPI-IBS patients.The level of I-FABP of healthy controls [(10.6 ± 8.2) μg/L] was also significantly lower than that of PI-IBS patients (P ＜ 0.05),yet no difference from that of NPI-IBS group.The I-FABP value of subgroup PI-IBS patients with diarrhoea (IBS-D) was significant higher than that of NPI-IBS group [(54.8 ± 9.3) μg/L vs (12.3 ± 6.2) μg/L,P ＜ 0.05].However,other parameters including gender,age,GSRS score,and I-FABP value of subgroup constipation (IBS-C) and mix (IBS-M),were not different between PI-IBS group and NPI-IBS group (all P ＞ 0.05).Conclusion PI-IBS is an occult intestinal inflammation disease with mucosa injury.I-FABP might be a potential testing marker for the diagnosis of PI-IBS.