Microspheres were generated after subjecting corn stem rind to highpressure water pretreatment. These microspheres can be divided into two categories according to their location: free microspheres and adsorbed microspheres. The formation and characterization of both microsphere types were studied. For the free microspheres, the maximum formation was reached at 180 °C; when the temperature was too high (200 °C) or too low (120 °C), no free microspheres were observed. As pretreatment temperature was varied, the morphologies of the free microspheres were different. For the adsorbed microspheres, their formation occurred over a wider temperature range, and their density increased with rising pretreatment temperature. Using Fourier transform infrared spectroscopy, many C=C and C=O bonds were identified on the surface of the free microspheres, indicating the presence of functional groups similar to those of lignin. Compared with untreated corn stem rind, the lignin signal of the residue surface was enhanced, which may be attributable to the increase in adsorbed microsphere quantity.