Knowledge of the function of growth-regulating factors (GRFs) in sugarcane (Saccharum officinarum and S. spontaneum) growth and development could assist breeders in selecting desirable plant architectures. However, limited information about GRFs is available in Saccharum due to their polyploidy. In this study, 22 GRFs were identified in the two species and their conserved domains, gene structures, chromosome location, and synteny were characterized. GRF7 expression varied among tissues and responded to diurnal rhythm. SsGRF7-YFP was localized preferentially in the nucleus and appears to act as a transcriptional cofactor. SsGRF7 positively regulated the size and length of rice leaves, possibly by regulating cell size and plant hormones. Of seven potential transcription factors binding to the SsGRF7 promoter in S. spontaneum, four showed positive expression patterns, and two showed negative expression patterns relative to SsGRF7.