Seijo is a name; notable people called Seijo include:

• Seijo Inagawa (1914–2007), Japanese yakuza boss, founder of the Inagawa-kai
• Bibiana Campos Seijo, editor, publisher, and media executive
• Francisco Zayas Seijo (born 1951), former member of the Puerto Rico House of Representatives
• Jorge Seijo (born 1942), radio and television personality
• Luisa Seijo (born 1950), Puerto Rican academic, activist, and social worker

• Seijo Gakuen Education Institute, educational institute that operates universities and schools in Japan
• Seijo Gakuen Junior High School and High School, private junior high and high school in Setagaya, Tokyo
• Lycée Seijo, Japanese boarding high school in Alsace region of France, near Colmar
• Seijo gakuen mae, railway station on the Odakyu Odawara Line in Setagaya, Tokyo, Japan
• Seijo University, private university in Seijo, Setagaya-ku, Tokyo, Japan
• Saijō (disambiguation)
• Seiji
• Siejo