• The storage root of sweetpotato is an important organ that has high economic and biological value, but little is known regarding its growth and development. In this study, we focused on the mechanisms of nitrogen (N) regulating storage root growth in sweetpotato. • Five sweetpotato cultivars were used to analyze the functions of N in regulating storage root growth. Growth responses and physiological indicators were measured to determine the physiological changes regulated by different N concentrations. Expression profiles of related genes were analyzed via microarray hybridization data and quantitative real-time polymerase chain reaction analysis to reveal the molecular mechanisms of storage root growth regulated by different N concentrations. • Our results indicated that N significantly affected sweetpotato root and shoot growth in the five cultivars studied. The root fresh weight of two of the sweetpotato cultivars, SS19 and GS87, was higher under low N concentrations compared with the other cultivars. SS19 and GS87 were found to be having greater tolerance to LN (low nitrogen) concentration. Several N response genes were involved in both N metabolism and storage root growth. • The present study provides greater understanding regarding the role of N in the regulation of storage root growth and offers impetus to better understand the mechanism of N involved in storage root growth in sweetpotato.