The researchers' aims were to determine the effect of perceived insufficient milk supply on the transition to supplementary food and the factors affecting it. This is a cross-sectional design study, we were conducted between April and August 2019 and included 335 mothers and their babies in a baby-friendly hospital in Turkey. It was shown that mothers with perceived insufficient milk switched to supplementary food 6.538 times more frequently (p < 0.05). It was shown that some maternal, lactational, and infant (baby's age) factors affected the perception of insufficient milk (p < 0.05). The perception of insufficient milk is an important factor contributing to the transition to supplementary food.