The blue crab, Callinectes sapidus, is the most important fishery resource of western Venezuelan in what concerns to landings and generation of foreign currency. In 2002 a new fishing gear was introduced, named long line, for the capture of the blue crab in Lake Maracaibo. Since the use of this new gear, the annual average landing in 2003 - 2008 doubled with respect to previous years (1998 - 2002) when pots were used, increasing from 5012 t to 10519 t. In this study, we evaluated the size structure of blue crabs in the landings before and after the use of the long line, based on monthly samplings of crabs during the period 2001 - 2007 in the main landing harbors and processing plants of Zulia state. Results indicated that the long line is less selective and extends the size range of crabs with respect to pots. In 2001 - 2002 the proportion of crabs with carapace width (CW) below 8.0 cm (minimal legal size) was 0.30% - 0.87% while for 2003 - 2007 it was 2.98% - 14.39% (in 2007). Average CW for 2001-2002 ranged between 9.3-9.4 cm while for 2003 - 2007 it ranged between 8.6 cm (2007) and 9.3 cm. The increment of catches of young, sexually immature crabs, below 8.0 cm CW, and the decrease of crabs average size in the landings with the use of long line, is a serious threat for the adequate renewal of the crab population. A better control and surveillance of the blue crab fishery in Lake Maracaibo is recommended.