Neurodegenerative diseases, particularly Alzheimer’s disease (AD), pose a significant global health challenge. The multifaceted impact of gut dysbiosis on neuroinflammation, oxidative stress, Aβ plaque formation, neurofibrillary tangles (NFTs) development, and blood–brain barrier (BBB) disruption needs to be delved into. Phytochemicals such as polyphenols, alkaloids, and terpenes are bioactive molecules that modify gut microbiota and affect AD pathogenesis. Compounds, such as resveratrol, curcumin, berberine, and quercetin, promote cellular autophagy, maintain gut and cellular homeostasis, and exhibit anti-inflammatory and anti-oxidant properties. The complex interaction between gut dysbiosis and Alzheimer's disease includes Aβ plaque formation, NFTs, and β-secretase activity, as well as the involvement of gut microbiota such as Bifidobacterium longum (NK46), which alleviates gut dysbiosis. This book chapter provides in-depth insights into the link between gut microbiota and neurodegenerative diseases to enhance the understanding of these complex illnesses and identify some effective therapeutic approaches.