In low-resource settings, where qualified health workers (HWs) are scarce and childhood mortality high, rational antimicrobial prescription for childhood illnesses is a challenge. To assess whether smartphones running guidelines, as compared with paper support, improve consultation process and rational use of medicines for children, a pilot cluster-randomized controlled study was conducted in Tanzania. Nine primary health-care facilities (HFs) were randomized into three arms: 1) paper algorithm, 2) electronic algorithm on a smartphone, and 3) control. All HWs attending children aged 2-59 months for acute illness in intervention HFs were trained on a new clinical algorithm for management of childhood illness (ALMANACH) either on 1) paper or 2) electronic support; 4 months after training, consultations were observed. An expert consultation was the reference for classification and treatment. Main outcomes were proportion of children checked for danger signs, and antibiotics prescription rate. A total of 504 consultations (166, 171, and 167 in control, paper, and phone arms, respectively) were observed. The use of smartphones versus paper was associated with a significant increase in children checked for danger signs (41% versus 74%, P = 0.04). Antibiotic prescriptions rate dropped from 70% in the control to 26%, and 25% in paper and electronic arms. The HWs-expert agreement on pneumonia classification remained low (expert's pneumonia identified by HWs in 26%, 30%, and 39% of patients, respectively).Mobile technology in low-income countries is implementable and has a potential to improve HWs' performance. Additional point-of-care diagnostic tests are needed to ensure appropriate management. Improving the rational use of antimicrobial is a challenge that ALMANACH can help to take up.