“The COVID-19 pandemic is far more than a health crisis: it is affecting societies and economies at their core,” warned by the UN. ActionAid Cambodia and BBC Media Action conducted a quantitative and qualitative study to assess the socio-economic impacts of the COVID-19 crisis on vulnerable workers in the informal sector in Cambodia to evidentially inform the Royal Government of Cambodia to tailor the response and recovery by ensuring no Cambodian citizen is left behind. To root our assessment at the grassroots level, ActionAid Cambodia collaborated with Building and Wood Workers Trade Union Federation of Cambodia (BWTUFC), Cambodian Food and Service Workers' Federation (CFSWF) and Independent Democracy of Informal Economic Association (IDEA) to assess the socio-economic impacts of COVID-19 crisis on mostly marginalized groups including workers in the entertainment sector, construction, transportation and street vendor. The study focuses on 416 workers in Phnom Penh and Siem Reap, and the field interviews were conducted in August 2020. We found these groups have been left behind by most of the existing interventions due to their mobility, working condition, and lack of coverage by a social protection scheme. More than economic impact, they have also experienced fearful uncertainty and family/career plan. Many of them need job, food and cash assistance, childcare, and other social protection/assistance.