Grand Jury Reform Act of 1998 - Amends rule 6 of the Federal Rules of Criminal Procedure to direct the court, upon impaneling a grand jury, to instruct and charge it on the rights, responsibilities, and duties of the grand jury. Grants the court the authority to investigate violations under such rule, including the authority to appoint counsel to investigate and report to the court regarding violations.

Directs that a witness subpoenaed to testify or produce information at any proceeding before a grand jury impaneled before a district court be given reasonable notice of: (1) the right to counsel; (2) privilege against self-incrimination; (3) the subject matter of the investigation; (4) whether the juror's conduct is under investigation; (5) the criminal statute the violation of which is under consideration (if known at the time); and (6) rights regarding immunity.

Allows the assistance of counsel for each witness subpoenaed to appear and testify, or to produce documents or other objects, before a grand jury in a district court during such time as the witness is questioned in the grand jury room. Provides for the appointment of counsel in the case of a witness who is determined by the court to be financially unable to obtain counsel.

Sets forth provisions regarding powers and duties of counsel, powers of the court, required disclosure of exculpatory evidence, and availability of grand jury transcripts and other statements.