[Objectives]  To find morphological characteristics that can accurately discriminate between the different instars of the aphid Semiaphis heraclei. [Methods]  Eight morphological indices of winged and wingless S. heraclei , including body length, body width, head width, antenna length, mesothoracic width, cornicle length, cauda length and hind tibia length, were measured. Multiple comparisons were performed to detect differences in the length or width of morphological characteristics using an LSD test. Correlations between the length or width of morphological characteristics and instar number were analyzed with linear regression. [Results]  The instars of S. heracleid (P < 0.01) differ significantly in all eight morphological characteristics measured. Indeed, there was no overlap in the antenna or hind tibia length of adjacent winged or wingless instars, which means that these measurements can unequivocally identify instars of both morphs. There was a small amount of overlap in cauda length between the 3rd and 4th wingless instars, and between the 4th instar and adults of the winged morph. Furthermore, the antennae of 1st instar larvae have 5 segments whereas all other instars have 6 segments. Thus, 1st instar larvae can be reliably identified from the number of antennal segments. Cauda length could be regarded as a typical index to differentiate between nymphs and adults. 3rd and 4th instars of the winged morph can also be identified by their expanded mesothorax and wing bud characteristics. [Conclusion]  The instars of S. heraclei can be quickly and reliably identified based on antenna length and hind tibia length. The cauda length, the number of antennae segment, wind bud and cauda development, also facilitate identifying the instars of this species.