The emergence of the coronavirus COVID-19 in December 2019 in Wuhan, China, affected all facets of people’s lives worldwide. As a result of the severity of the pandemic, governments worldwide adopted several policies and containment measures, such as social isolation, especially for vulnerable populations, including older adults. This study aimed to explore these older adults’ experiences of social isolation during COVID-19. A systematic review method based on the PRISMA protocol was used, and five databases (EMBASE, PsycINFO, PsycEXTRA, CINAHL, and Medline) were comprehensively searched. Studies were limited to those published between 2020 and 2023. Thirteen qualitative studies met the inclusion criteria and were analysed thematically. A thematic analysis identified the following five major themes: intense feeling of loneliness due to social isolation; use of social media as a coping mechanism during social isolation; anxiety during social isolation; fear during social isolation; and financial security during social isolation. This review provides useful information on how to mitigate the effects of social isolation on the elderly population during future public health crises.