Abstract: Post-translational modification by small ubiquitin-related modifiers (SUMOs) is an important regulatory process to modulate protein function. This paper summarizes the SUMOylation pathway in plants; the pathway consists of SUMO molecules, a SUMO conjugation enzyme cascade and de-conjugation enzymes. Nascent SUMOs are processed by SUMO-specific proteases, then mature SUMOs are conjugated to substrate proteins by sequential action of three groups of enzymes: SUMO-activating enzymes (E1), SUMO-conjugating enzymes (E2) and SUMO-ligating enzymes (E3). SUMOylation can be reversed by SUMO-specific proteases. SUMO modification in plants is involved in flowering induction, hormone signaling, pathogen defense and stress response.