  We report the Sr substitution effect in an antiferromagnetic insulator
LaMnAsO. The Sr doping limit is $x\sim$ 0.10 under the synthesis conditions, as
revealed by x-ray diffractions indicate. Upon Sr doping, the room-temperature
resistivity drops by five orders of magnitude down to $\sim$0.01
$\Omega\cdot$cm, and the temperature dependence of resistivity shows
essentially metallic behavior for $x\geq$0.08. Hall and Seebeck measurements
confirm consistently that the insulator-to-metal transition is due to hole
doping. Strikingly, the room-temperature Seebeck coefficient for the metallic
samples is as high as $\sim240 \mu$V/K, making the system as a possible
candidate for thermoelectric applications.
