Raising a child with autism spectrum disorder is a challenging experience that can impact maternal well-being. This daily diary study investigates (1) the relationship between daily stress, general life stress as well as stress related to the child's characteristics, and daily negative affect, (2) the role of daily positive affect in promoting resistance to stress and recovery from daily stress, (3) the moderating effects of optimism and perceived control on the relationships between daily stress, daily positive affect, and daily negative affect, and (4) whether daily positive affect serves to mediate both relationship between optimism and daily negative affect, as well as the relationship between perceived control and daily negative affect. Results from hierarchical linear models (HLM) revealed that higher levels of perceived stress were associated with decreased well-being, both within and across days. Daily positive affect buffered the immediate and longer-lasting negative impact of perceived stress; however, this occurred only one days of low to moderate levels of stress. Although optimism and perceived control did not explain differences in the daily relationships previously described, each of these personality characteristics helped explain the degree to which positive affect is generated. Implications of the present study are discussed with regard to theoretical models of positive affect and the development of intervention programs. Directions for future research are also discussed.