Barrichello was almost one second faster than Nico Rosberg in a Williams.
The McLaren of reigning world champion Lewis Hamilton managed 1:20.869 among his 70 laps, giving him the eighth fastest time but nearly two seconds behind Barrichello.
In terms of times achieved, it has been a poor week for McLaren.
The 2009 season gets underway in Melbourne on March 29.
Barcelona test times
Rubens Barrichello (BRA) Brawn GP 1:18.926 (110 laps)
Nico Rosberg (GER) Williams 1:19.774 (120)
Timo Glock (GER) Toyota 1:20.091 (128)
Sebastian Vettel (GER) Red Bull 1:20.576 (83)
Fernando Alonso (ESP) Renault 1:20.664 (64)
Felipe Massa (BRA) Ferrari 1:20.677 (92)
Robert Kubica (POL) BMW 1:20.740 (134)
Lewis Hamilton (GBR) McLaren 1:20.869 (70)
Sebastien Buemi (SUI) Toro Rosso 1:21.013 (62)
Giancarlo Fisichella (ITA) Force India 1:21.045 (141)
Sebastien Bourdais (FRA) Toro Rosso 1:21.629 (27)
The McLaren of reigning world champion Lewis Hamilton managed 1:20.869 among his 70 laps, giving him the eighth fastest time but nearly two seconds behind Barrichello.
In terms of times achieved, it has been a poor week for McLaren.
The 2009 season gets underway in Melbourne on March 29.
Barcelona test times
Rubens Barrichello (BRA) Brawn GP 1:18.926 (110 laps)
Nico Rosberg (GER) Williams 1:19.774 (120)
Timo Glock (GER) Toyota 1:20.091 (128)
Sebastian Vettel (GER) Red Bull 1:20.576 (83)
Fernando Alonso (ESP) Renault 1:20.664 (64)
Felipe Massa (BRA) Ferrari 1:20.677 (92)
Robert Kubica (POL) BMW 1:20.740 (134)
Lewis Hamilton (GBR) McLaren 1:20.869 (70)
Sebastien Buemi (SUI) Toro Rosso 1:21.013 (62)
Giancarlo Fisichella (ITA) Force India 1:21.045 (141)
Sebastien Bourdais (FRA) Toro Rosso 1:21.629 (27)