Infection with enterotoxigenic Escherichia coli (ETEC) is an important health threat for weaning piglets. As tannins limit E. coli infection, a study was set up to assess the efficacy of Sainfoin (Onobrychis viciifolia) tannins to reduce ETEC infection symptoms in post weaning diarrhea (PWD). Twenty Swiss Large White piglets from four litters weaned at 23 (±1) days with an average BW of 8.6 (±0.6) kg were included in this study. Piglets were randomly assigned by bodyweight (BW) to two groups, and housed by group in pen of 10. The Control group (C; n=10) had ad libitum access to a standard starter diet formulated according to the Swiss feeding recommendations for weaned pigs. The treatment group (T; n=10) was offered a starter diet containing 12.6% Sainfoin, corresponding to a Condensed Tannins (CT) concentration of 1%. The two diets contained the same ingredients (except Sainfoin) and were formulated to be isocaloric (13MJ/kg) and isonitrogenic (165g/kg). Four days after weaning, C and T pigs were infected with an ETEC F4 strain. Fecal score (n=9), BW (7) and ETEC shedding (6) were regularly measured throughout the study until 10 days after infection. Diarrhea was defined as a fecal score of 3 or above on a scale of 1 (no diarrhea) to 4 (watery diarrhea). Duration of diarrhea was the sum of days in diarrhea. Fecal score was analyzed with a two-way ordinal regression whereas individual BW, average daily gain (ADG) and duration of diarrhea with two way (repeated) measures ANOVA. Sainfoin tannins reduced fecal scores (P=0.003) and the duration of diarrhea (P=0.002). The ADG did not differ between C and T pigs (P = 0.633). The CT from Sainfoin seem to be efficient to overcome PWD caused by ETEC infection. Further studies are required to refine Sainfoin CT dose for an optimal efficiency.