Well this depends on several things, professional Baseball refers to both the major and minor leagues. The minor leagues are those divided into AAA AA, etc, and most are associated with major league teams. Like the Memphis Red Birds are a AAA team and when they go to the Majors they move up to the St. Louis Cardinals.
So my first question is: are you referring to the major or minor leagues? and if minor? Which division? Or all of professional baseball as a whole?
Secondly: Are you referring to an individual players losing streak? or an entire teams losing streak?
Thirdly: Consecutive games in a season? Or consecutive seasons lost - World Series lost that is?
1st longest; 'bout 26 2nd longest; 'bout 24
parshaves
18 games in 1982
12 games
9 as of 8/5/12
Cleveland cavaliers 26
towson university
11 games in 63-64
Them Tampa Bay had a losing streak of 26, from 1976-1977. 0-14 in 1976 and 0-12 1977
The longest losing streak in Chicago Bears history is 14 games, which occurred between 1976 and 1977. During this period, the team struggled significantly, culminating in a winless 1976 season. This streak remains a notable low point in the franchise's history.
Make that 18 seasons (1992 - 2010) and counting.
29