Occurrence behavior of microexplosion in droplet combustion of fuel mixtures is studied. Experiments were performed using unsupported droplets of n-alkane/n-hexadecane mixtures in normal gravity. It was found that the occurrence of microexplosion is stochastic and cannot be predicted by the classical criterion for microexplosion occurrence using the limit of superheat and the droplet temperature. An occurrence model for the microexplosion based on the homogeneous nucleation theory is presented and shows that the occurrence probability of the microexplosion is determined by the ratio of the liquid phase lifetime to the nucleation time during the quasi-steady vaporization period. The nucleation time is inversely proportional to the nucleation time is inversely proportional to the nucleation rate and superheated liquid volume. The relative value of the droplet temperature and the limit of superheat affects the occurrence probability through the nucleation rate. It can be well explained by the model that the occurrence probability has the maximum value for a certain initial concentration of the fuel mixture.