Two carborane-containing resol phenolic resins (P

1

and P

2

) with high boron content were synthesized

via

the reaction of carborane bisphenols (

1

and

2

) with formaldehyde in the presence of alkaline. HRMS results indicate that P

1

is mainly composed of hydroxymethylated

o

-carborane bisphenols

the

M

w

of which was restrained around 500 due to the strong steric hindrance of o-carborane bisphenol. In contrast

the molecular weight of P

2

was well regulated under various reaction conditions. The obtained resins were characterized with spectroscopic techniques including FTIR

1

H-NMR

13

C-NMR

and

11

B-NMR

which gave satisfactory results. TGA studies show that P

2

shows char yield of 88.9% and 92.9% at 900 ℃under nitrogen and air respectively. The imported carborane cage endows phenolic resin with ultrahigh char yield. Particularly

the char yield of the obtained carborane-containing phenolic resin under air is higher than that under nitrogen. FTIR and XRD confirm that the carborane cage could react with oxygen to form B

2

O

3

at elevated temperatures

which postpones the thermal decomposition of phenolic resin and accounts for the high char yield.