In great efforts to utilize alternative iron ore resources in sintering process, it was attempted to use magnetite concentrate as an additive in adhering fines of quasi-particle and the effect of magnetite addition on assimilation behavior was investigated. A basic study was performed using the synthetic mixture of typical sinter composition with focus on the phase formation behavior of sinter. With small addition of magnetite, it was found that the formation of SFCA was increased with fixed CaO because Fe²⁺ probably replaced Ca²⁺ in the substitution mechanism of SFCA. Then the research was further extended by adopting quasi-particle concept using actual iron ores as a case study. Samples of coupled ore tablets simulating quasi-particle structure were prepared and experiments were carried out to investigate how magnetite addition affects the assimilation behavior of quasi-particle. Based on the experimental results and analysis, it was found that the small amount of magnetite addition, more specifically Fe²⁺ in magnetite, significantly influenced the physicochemical properties of melt as well as the structure of SFCA. The highest melt penetration depth was observed in N90-J10 sample containing 10 mass% magnetite ore J. As a result, it was concluded that the assimilation behavior was improved with proper amount of magnetite addition in adhering fines of quasi-particle.