Gratitude and optimism are positive psychological dispositions associated with beneficial outcomes. To examine their associations with physiological and psychological experiences in daily life, we examined data from an Ecological Momentary Assessment study (N = 4,825), including blood pressure, heart rate, and reports of stress, health behaviors, and thoughts. Trait gratitude and trait optimism both predicted lower heart rate and blood pressure, better sleep quality, more exercise, less stress, more positive expectations and reflections, and greater feelings of appreciation toward others. However, gratitude and optimism were not completely overlapping constructs: Gratitude was a stronger predictor of felt appreciation toward others and pleasantness when reflecting on the best part of the day, whereas optimism was a stronger predictor of sleep quality, lower stress, and lower unpleasantness when reflecting on the worst part of the day. These associations reveal both similar and differential influences of positive dispositions on psychological and physiological outcomes that provide insight into health consequences. (PsycInfo Database Record (c) 2021 APA, all rights reserved).