∵x1、x2是方程x2+6x+3=0的两实数根,根据x1+x2=-
b
a,x1•x2=
c
a,
∴x1+x2=-6,x1x2=3,
∴x12+x22=(x1+x2)2-2x1x2=36-6=30,
故答案为:30.