Hemiparesis is one of the most common disabling impairment in post-stroke people. However, studies on the assessment of hemiparesis have paid little attention to the metabolism status of limb muscles. In this work, a non-invasive muscle oxygenation monitoring technique, near-infrared spectroscopy (LAIRS) was used to acquire concentration of oxy-hemoglobin (HbO₂) and total-hemoglobin (tHb) in four hemiparesis patients. The participants were divided into two groups. Participants who can clench their paretic side of fist were attributed to mild group and asked to perform clenching tasks using their nonparetic or paretic hand alternatively. Participants who cannot clench their paretic side of fist were attributed to severe group and asked to only perform clenching tasks using their non-paretic hand. The analysis of muscle oxygenation variation showed that the HbO₂ and tHb decreased on the contracted side while no significant HbO₂ and tHb changes were observed on the noncontracted side at mild group. For severe group, the HbO₂ contraction of the paretic side was observed to decrease when performing non-paretic fist clenching. These results indicated that the muscle oxygen variation at the paretic side was different due to the severity of hemiparesis and it may be a potential assessment for hemiparesis.