Abstract: Aphids establish compatible interaction with host plants through overcoming plant defenses and manipulating plant metabolism for successful feeding and reproduction. This usually causes changes to cellular structures and plant growth and development. With the aim to understand the effect of green peach aphid infestation on apricot leaf cell differentiation，internode elongation，and flower bud formation，ultrastructures of infested and uninfested young leaves as well as internode length and flower bud number per node of infested and uninfested shoots were compared. Main findings are as follows：（1）The mesophyll cell in the infested young leaf is apparently smaller and shorter than that in the uninfested leaf of the same age. This implies that the mesophyll cell grows much slower in the infested young leaf than in the uninfested young leaf.（2）Plastids in the mesophyll of the infested and uninfested young leaves of the same age reveal remarkably different morphological and structural features. Plastids in the mesophyll cells of the infested young leaf are small，take a spherical or elliptical shape，contain few thylakoids，lack typical grana，and rarely contain starch grains. In contrast，plastids in the mesophyll cells of the uninfested young leaf of the same age are larger，take a lens-like shape，contain rich thylakoids as well as a lot of typical grana，and accumulate a large amount of starch. The differences in shape and structure indicate that the conversion of proplastids into chloroplasts is rapid in the mesophyll of the uninfested leaf，whereas the process takes a much longer time in the infested leaf.（3）The internode of the infested shoot is dramatically shorter than that of the uninfested shoot，while the node of the infested shoot bears significantly more flower buds than that of the uninfested shoot. Therefore，it is suggested that aphid infestation retard cell enlargement and chloroplast development，inhibit internode elongation，but promote flower bud formation.