COVID-19 can cause long-term symptoms, such as a post-infection syndrome, known as Long-COVID. Among the symptoms present during this period, the most reported are gastrointestinal symptoms. This study discusses the effects of changes in the gut microbiota of post-COVID-19 patients. SARS-CoV-2 infection is associated with significant alterations in gut microbial composition, disturbing its homeostasis and promoting a reduction in the abundance of beneficial symbiotic bacteria and an increase in the abundance of opportunistic pathogens. Furthermore, the composition of the gut microbiota may play a role in the prognosis of patients with post-COVID-19 infection. The microbiota of the intestinal tract and the respiratory tract influence each other; therefore, the gut–lung axis has attracted increasing interest in understanding COVID-19. Moreover, the brain–gut axis has been studied, since there have been reports of anxiety and depression along with post-COVID-19 gastrointestinal symptoms. Treatments options for intestinal dysbiosis in Long-COVID patients include probiotics, prebiotics, and fecal microbiota transplantation. These treatments may serve as an approach to improve gastrointestinal symptoms during Long-COVID, increasing microbiome diversity, strengthening the integrity of intestinal barrier functions, and consequently influencing the treatment of COVID-19.