Ratajczak is a Polish surname. It is a patronymic surname of Northern Polish origin formed by the addition of the diminutive suffix -czak to the patronymic nickname or surname Rataj lit. 'farmer'. It may refer to:

• Alicja Ratajczak (born 1995), Polish cyclist
• Dariusz Ratajczak (1962–2010), Polish historian
• Donald Ratajczak (born 1942), American economist
• Elżbieta Ratajczak (born 1946), Polish politician
• Jacek Ratajczak (born 1973), Polish footballer
• Michael Ratajczak (born 1982), German footballer
• Kevin Ratajczak (born 1985), German singer