In a sample 110 Mexican origin infants (M = 7.24; SD = 2.06; range, 3.78 - 13.04) we examine the bidirectional covariation of mother and infant positive and negative affect across the day. Further, we examine maternal emotion regulation as a potential moderator of the linkage between mother-infant affect, and infant-mother affect. Using an Ecological Momentary Assessment design, mothers reported on their positive and negative affect three times a day, for six days. Analyses employed a multi-level modeling approach to examine moment-to-moment covariation. Results indicated both mother and infant negative affect, and mother and infant positive affect to significantly covary. Interestingly, maternal emotional regulation did not moderate either the covariation of negative or positive mother-infant affect. These analyses represent one of the first examinations of daily covariation in mother-infant dyadic affect.