1048 (MXLVIII) was a leap year starting on Friday of the Julian calendar, the 1048th year of the Common Era (CE) and Anno Domini (AD) designations, the 48th year of the 2nd millennium, the 48th year of the 11th century, and the 9th year of the 1040s decade. As of the start of 1048, the Gregorian calendar was 6 days ahead of the Julian calendar, which was the dominant calendar of the time.

• The city of Oslo is founded by King Harald Hardrada of Norway.
• Battle of Pasinler – Seljuks defeat a force of Byzantines and Georgians.
• Pope Benedict IX is driven out of Rome, ending his third and final pontificate.

• May 18 – Omar Khayyam, Persian poet and mathematician (died 1134)
• date unknown
  • Michael IX Comneus, Byzantine emperor (died 1088)
  • Pope Paschal II (died 1118)

• Pope Damasus II (born 1000)