Studies show that having greater weight-for-length in infancy and obesity in childhood can lead to obesity in adolescence and adulthood. Reducing obesity risk factors may decrease one’s chance of developing obesity. This longitudinal observational study’s objective was to investigate longitudinal associations of infant nighttime sleep proportion with gut microbiome diversity and taxa abundance (n=30). Fecal samples, sleep diaries and sleep actigraphy were taken at 3 and 8 weeks, and 3, 6, 9, and 12 months during infancy. Diversity analysis was completed in Quantitative Insights Into Microbial Ecology 2 (QIIME 2.0) in conjunction with PERMANOVA tests for group comparisons. QIIME2 diversity plug-ins were used to calculate alpha diversity (Shannon index) and beta diversity (Unweighted UniFrac distance) metrics. Percent abundance values for bifidobacteria and lactobacillus were exported at the genus level for subsequent analyses. Mixed linear models (MLM) and Adonis multiple regression analyses were used to test for significant (alpha = 0.05) effects of nighttime sleep fraction on alpha and beta diversity metrics and abundance of specific microbial taxa. All statistical models accounted for individual effects (baby/subject ID), time, and a time*sleep fraction interaction. For aim 1, the regression model was: Shannon = baby + time + sleep fraction + time*sleep fraction. The overall regression was statistically significant (R2 = 0.518, F = 3.9576, p < 0.0001). Nighttime sleep proportion did not significantly predict gut microbiome richness in infants (β = 0.281, p = 0.8603). For aim 2, when adjusting for covariates in a multiple regression model, sleep fraction was insignificant. The R2= 0.005106, F= 0.810996, p=0.619). For aim 3, the fitted regression models were Bifidobacteria/Lactobacillus= baby + time + sleep fraction + time*sleep fraction. The overall regression for Bifidobacteria was statistically significant (R2 = 0.371944, F = 2.6286, p = 0.0008) but nighttime sleep proportion did not significantly predict Bifidobacteria abundance in infants (β = -54.40518, p = 0.2723). The overall regression for Lactobacillus was statistically significant (R2 = 0.236381, F = 1.8687, p = 0.0208) but sleep fraction was not associated with taxa abundance. Further research is needed to describe associations between sleep, gut microbiome, and the distal outcome of obesity.