The firm has given the BlackRock Scientific Australian Shares Fund strategy an investment grade recommendation.
The fund's previous rating was highly recommended.
"We can't maintain the same conviction level in BlackRock's scientific Australian equities strategy at present after the departure of a number of key team members," a Morningstar report said.
The departures included the resignation of portfolio managers Glen Harris and Nick Burt.
Global chief investment officer of the strategy Morry Waked also announced his resignation last month.
Following the changes, BlackRock reshuffled the team and appointed Andrew Jackson as head of Australian investments.
David Walsh will also take over the portfolio management duties following Waked's resignation.
Walsh has worked for the firm since 2000, a period which included time with the recently merged Barclays Global Investors (BGI).
At BGI he was a senior strategist for all international equity strategies.
The firm has also internally appointed Paddy McCrudden to the Australian scientific active equities team to work with Walsh.
McCrudden has been with BGI
since 2001.
The new team would need to prove itself following the key departures, Morningstar said.
However, it said the inclusion of the Melbourne-based BlackRock quantitative team meant adequate resourcing was in place.
"We will be watching the integration and development of the new team closely and revisiting our opinion of the BlackRock Australian shares strategy in mid-2010," it said.
