Sustainable livelihood is not only the livelihood objective but also households’ expectations. Livelihood diversification is aimed at ensuring the farmer's resilience to shocks and improving livelihood sustainability. Research on livelihood diversification in rural areas contributes to the development of agricultural development policies, social security policies for all farm households in Vietnam. The authors applied statistic and regression methods to analyze VARHS’s database which is surveyed 12 provinces in Vietnam over years. This paper is carried out to analyze and evaluate factors affecting the probability of choosing to diversify the livelihoods of Vietnamese farmers by developing a diversification index (SID) and SID’s determinants based on the DFID framework. The results show that the decision to diversify livelihood is influenced by many factors, including age, planted areas, asset value, saving money. Since then, the authors propose some implications for promoting the livelihood diversification of Vietnamese farmers.