The effects of succinylation on emulsifying property and the in vitro trypsin digestibility of kidney bean protein isolate (KPI) were investigated. The succinylation of KPI included two stages: one is the succinylation of ζ-amino groups (N- succinylation) and the other is the succinylation of hydroxyl groups (O-succinylation). The degree of the N-succinylation sharply increased to about 93~94% with the anhydride levels increasing from 0 to 0.2. The O-acylation (Thr, Ser) distinctly occurred only when the N-acylation was nearly complete. The O-acylation occurred only after extensive blocks of ζ-amino groups. At low ionized strength, the EAI and EAS increased as the degree of N-succinylation, while the EAI and EAS of succinylated KPI were nearly unaffected in N-succinylation. The EAI and ESI of untreated or succinylated KPI decreased as the ionized strength of the tested solution increased. Additionally, the in vitro trypsin digestibility was improved by the succinylation in a dose-dependent manner. The present data indicated that the succinylation could be used to modulate the emulsifying and in vitro digestibility of kidney bean protein isolate (KPI).