Background: What is the appropriate time to start complementary feeding for preterm infants? The answer to this question is yet under debate. The timing of initiating complementary feeding may be associated with overweight in term infants. This systematic review aimed to study the effect of the timing of initiating complementary feeding on overweight in preterm infants. Predefined search items included preterm infants, complementary feeding, overweight, and their synonyms. Summary: The search identified 15,749 articles, of which 5 articles were included. Three studies presented data of randomized controlled trials and 2 studies were cohort studies. Two randomized controlled trials found no significant difference in body mass index (BMI) Z-score between the intervention groups at 12 months of age. One randomized controlled trial presented a significant greater mean rate of growth in length per week until 12 months in the preterm weaning strategy-group compared with the current best practices. One observational study concluded that each month the infants received complementary food later, the Z-score for length and weight was reduced by 0.1. Key Messages: No clear conclusion could be drawn from the included studies. This review illustrates the need for further research to access the effect of the timing of initiating complementary feeding on overweight in preterm infants.