Gut colonization represents the main source for KPC-producing Klebsiella pneumoniae (KPC-Kp) epidemic dissemination. Oral gentamicin, 80 mg four times daily, was administered to 50 consecutive patients with gut colonization by gentamicin-susceptible KPC-Kp in cases of planned surgery, major medical intervention, or need for patient transfer. The overall decontamination rate was 68% (34/50). The median duration of gentamicin treatment was 9 days (interquartile range, 7 to 15 days) in decontaminated patients compared to 24 days (interquartile range, 20 to 30 days) in those with persistent colonization (P<0.001). In the six-month period of follow-up, KPC-Kp infections were documented in 5/34 (15%) successfully decontaminated patients compared to 12/16 (73%) persistent carriers (P<0.001). The decontamination rate was 96% (22/23) in patients receiving oral gentamicin only, compared to 44% (12/27) of those treated with oral gentamicin and concomitant systemic antibiotic therapy (CSAT) (P<0.001). The multivariate analysis confirmed CSAT and KPC-Kp infection as the variables associated with gut decontamination. In the follow-up period, KPC-Kp infections were documented in 2/23 (9%) of patients treated with oral gentamicin only and in 15/27 (56%) of those also receiving CSAT (P=0.003). No difference in overall death rate between different groups was documented. Gentamicin-resistant KPC-Kp strains were isolated from stools of 4/16 persistent carriers. Peak gentamicin blood levels were below 1 mg/liter in 12/14 tested patients. Oral gentamicin was shown to be potentially useful for gut decontamination and prevention of infection due to KPC-Kp, especially in patients not receiving CSAT. The risk of emergence of gentamicin-resistant KPC-Kp should be considered.