Aung San Suu Kyi, the Nobel Peace Prize laureate who spent years in home confinement, urged members to maintain a united front, The Wall Street Journal reported. She spoke at the opening ceremony in a Yangon restaurant.
"Our country is a union, and that is why our party's unity is very important," she said. "To be united in a diverse group is very important for our country."
Myanmar, the country formerly known as Burma, holds elections in 2015. Suu Kyi is considered a likely presidential contender, although she might be barred from running by a law requiring candidates to have no foreign relatives.
Since the military junta installed a nominally civilian regime, some have criticized the NLID, saying it has given up on its founding goal of establishing real democracy in Myanmar. Others are unhappy about changes in party rules that require the central committee to be elected by state when, in the past, most leaders were from Yangon, the city formerly known as Rangoon.
"Now, our processes are changing, our members are selected from rural, township and other division areas in accordance with democratization," Suu Kyi told delegates. "I know that some members are not happy about this, but you cannot fault democracy."
The party was founded in 1988 during a period of political unrest. When it won 80 percent of parliamentary seats in 1990 in the country's first free election in three decades, the junta cracked down on it and on Suu Kyi.