To investigate the effects of Chlorella alga on gut microbiota dysbiosis in type-2 diabetes (T2D). The stress perception of patients was also investigated. Chlorella (3 g/day) was administered to patients with T2D (n = 10) for a period of 30 days. Gut microbiota composition was analysed by 16S rDNA gene sequencing, and stress perception was evaluated using the perceived stress scale (PSS). A total of 13 phyla, 89 families, and 185 genera were identified from all faecal samples of patients with T2D, and Firmicutes and Bacteroidetes were the most dominant phyla among all samples. Chlorella decreased Bacteroidetes and increased Firmicutes. The proportions of the Akkermansia, Coprococcus, Dorea, Lachnospira, Phascolarctobacterium, and Ruminococcus generas increased, whereas the proportion of Paraprevotella, Prevotella, Klebsiella, and Sutterella decreased in the faeces of patients with T2D after Chlorella intake. Chlorella induced a significant reduction in perceived stress in patients with T2D, and better PSS scores negatively correlated with an increase in Akkermansia, Coprococcus, Dorea, Lachnospira, Phascolarctobacterium, and Ruminococcus and positively correlated with a decrease in Paraprevotella, Prevotella, Klebsiella, and Sutterella. Altogether, these results show the ability of Chlorella to positively modulate gut dysbiosis, leading to reduced stress perception in patients with T2D. Our findings contribute to the globally increasing search for new preventive and therapeutic strategies aimed at restoring the balance of the intestinal ecosystem.