The 1971 - 1972 Los Angeles Lakers still own the longest winning streak with 33 straight wins. There first win of the streak happened on November 5, 1971 and lasted until the fell to the Milwaukee Bucks on January 9, 1972. The Lakers went on to win the NBA Championship that year.
Before the Lakers set the mark at 33 games, the previous record of 20 straight wins was set by the Washington Capitals over two seasons. They won the last 5 regular season games of the 1947-1948 season and the first 15 games of the 1948-1949 season. The Milwaukee Bucks tied the mark with 20 straight wins during the 1970-1971 NBA season.