A statement from the NDP says Shane Simpson had surgery a day after he was admitted for abdominal pain.
The party says the entire tumour was removed, but it won't be clear for a while whether it is malignant or benign.
The 59-year-old caucus chairman for the New Democrats was first elected to the legislature in 2005 and is the Opposition critic of the government's core review of government programs and spending.
Simpson also has critic duties for gaming, liquor modernization and the BC Pavilion Corporation
He sits on the legislative management committee, which deals with MLA expense disclosures.