Reeva Steenkamp's family said in a statement that her mother, June, and "other family members" will be at the trial in Pretoria, which starts on March 3. No members of Ms Steenkamp's immediate family have attended any of the previous legal proceedings.
Ms Steenkamp was shot dead by Pistorius on February 14 last year. The world-famous athlete denies murder.
The Steenkamp family's statement added that "all we are looking for is closure and to know that our daughter did not suffer on that tragic Valentine's Day".
The family released the statement "as the first anniversary of our beloved daughter's death approaches" on Friday.