Khar, 34, this week became Pakistan`s youngest and first woman Foreign Minister. But Rehman said the decision to give the slot to a woman cannot be called a wise decision.
"We have reservations over the decision and we do not know who she will represent (Pakistan) on the diplomatic front," he told reporters at parliament yesterday.
Rehman said Khar is a businesswoman and "does not have any diplomatic and political experience" and pointed out that she would now face an experienced and wise leader in S M Krishna when she travels to India for talks.
Khar was appointed by President Asif Ali Zardari on the advice of Prime Minister Yousuf Raza Gilani and both leaders praised her shortly after she took oath as the country`s 26th Foreign Minister.
She will have important engagements in coming days, including ministerial-level talks in New Delhi on July 27.
Khar will travel to Indonesia this week to attend an ASEAN conference, where she is expected to meet US Secretary of State Hillary Clinton and the Chinese Foreign Minister on the sidelines of the meet.
Referring to the upcoming talks with India, Rehman said Khar will face a "very senior, experienced and wise" leader when she meets Krishna on July 27.
"What priorities will our new Foreign Minister have and how will she fight Pakistan`s case?" said Rehman, who heads a special parliamentary committee on Kashmir.