The aim was to evaluate the levels of aflatoxin M1 (AFM1), ochratoxin A (OTA), zearalenone (ZEN), deoxynivalenol (DON) in human milk, and to investigate the relation between selected mycotoxin levels in breast milk and infantile growth in exclusively-breastfed infants under four months. Mycotoxin analysis was performed with commercial ELISA kits. Infants were weighed, and z scores of weight-for-age (WAZ) were calculated with WHO standards. The first quartile of the mycotoxin levels was classified in subgroups as low-level, the last quartile as high-level, and between them as middle-level. The subgroups of AFM1, OTA, and DON had similar infants’ WAZ. When cases without maternal smoke exposure were selected and WAZ at birth, infant age, and gender were adjusted, higher infant WAZ on admission was detected in high-ZEN subgroup (p = 0.033). Further cohort studies in exclusively-breastfed infants and absence of maternal smoke exposure could clarify the effect of ZEN on infant growth.