(1) Background: The human gut microbiome may regulate sleep through the gut–brain axis. However, the sleep-promoting effects of gut microbiota remain unclear. (2) Methods: We obtained sleep–wake profiles from 25 rats receivingP. histicola(P. histicolagroup), 5 rats receivingP. stercorea(P. stercoreagroup), 4 rats not receiving bacteria (No administration group), and 8 rats receivingP. histicolaextracellular vesicles (EV) (EV group) during the baseline, administration, and withdrawal periods. (3) Results: TheP. histicolagroup showed increased total sleep, rapid eye movement (REM) sleep, and non-rapid eye movement (NREM) sleep time during the administration and withdrawal periods; on the last day of administration, we found significant increases of 52 min for total sleep (p< 0.01), 13 min for REM sleep (p< 0.05), and 39 min for NREM sleep (p< 0.01) over the baseline. EV administration also increased NREM sleep time on Day 3 of administration (p= 0.05). We observed a linear trend in the dose–response relationship for total sleep and NREM sleep in theP. histicolagroup. However, neither the no-administration group nor theP. stercoreagroup showed significant findings. (4) Conclusions: Oral administration of probioticP. histicolamay improve sleep and could be a potential sleep aid. Further rigorous evaluations for the safety and efficacy ofP. histicolasupplementation are warranted.