Background: Antimicrobial resistance is a serious threat to the global achievements in child health thus far. Previous studies have found high use of antibiotics in children in Northern Tanzania, but the experiences of the primary care-givers, who play a key role in accessing and administering antibiotics for the sick child, has remained largely unknown. We aimed to understand mothers’ conceptions of antibiotic use in their children, which is of importance when forming strategies to improve antibiotic use in the community. Method: A qualitative study including eight focus group discussions with mothers of under-five children in Moshi urban and rural districts, Northern Tanzania, was performed during 2019. The discussions were recorded, transcribed verbatim, translated to English and analysed according to the phenomenographic approach. Findings: Three conceptual themes emerged during analysis; (1) conceptions of disease and antibiotics, (2) accessing treatment and (3) administering antibiotics. Antibiotics were often perceived as a universal treatment for common symptoms or diseases in children with few side-effects. Although mothers preferred to attend a healthcare facility, unforeseen costs, long waits and lack of financial support from their husbands, pose barriers for care-seeking. However, pharmacies were perceived as a cheap and convenient option to access previously used or prescribed antibiotics. Some mothers sought advice from a trusted neighbour regarding when to seek care, thus resembling the function of the community health worker (CHW). Conclusions: To improve antibiotic use in children under five years of age in Northern Tanzania, we suggest targeting behaviour of individuals alone will not be sufficient. Improving structures, including the healthcare system and socio-economic inequality, are needed for sustained results. In the meantime, equipping CHWs to support women in appropriate healthcare seeking for their children, may be a feasible target for intervention.