This paper aimed at developing an index, called Sleep Index, to assess the quality of sleep in normal and obstructive sleep apnea (OSA) subjects. The Sleep Index was designed to be directly proportional to the summation of product of the number seconds spent in each stage of sleep and the selected weighting coefficient of each sleep stage. It was also inversely proportional to the product of total number of sleep stage shifts and the total number of seconds spent in all stages of sleep. In order to test the proposed index, data from eleven previously diagnosed sleep apnea subjects (6 females and 5 males; Age: 50 ± 8.94; Body Mass Index (BMI): 31.70 ± 6.97) and 14 normal subjects (8 females and 6 males; Age: 46.43 ± 9.61; BMI: 25.541± 3.061) were used. All the subjects underwent nocturnal polysomnography (NPSG) at an accredited sleep center. Statistical testing of the Sleep Index showed that its mean was significantly different for normal and OSA subjects (p<0.04). The Sleep Index values were higher for normal subjects than for sleep apnea subjects. This was in part due to the higher number of sleep stage shifts in OSA subjects compared to normal subjects. Therefore, higher Sleep Index values reflect better sleep quality. The number of sleep stage shifts should be higher for sleep apnea subjects as they frequently experience sleep arousal and sleep continuity is impaired, resulting in daytime sleepiness.