Ratajczak is a Polish-language surname. It is a patronymic surname of Northern Poland origin formed by the addition of the diminutive suffix "-czak" to father's nickname or surname "Rataj", "farmer" (historical term). It may refer to:

• Alicja Ratajczak (born 1995), Polish cyclist
• Dariusz Ratajczak (1962–2010), Polish historian
• Donald Ratajczak (born 1942), economist
• Elżbieta Ratajczak (born 1946), Polish politician
• Jacek Ratajczak (born 1973), Polish footballer
• Michael Ratajczak (born 1982) German footballer