For McMullen maps f
λ
(z) = z
p
+ λ/z
p
, where
λ
∈
C
\
{
0
}
, it is known that if p ⩾ 3 and λ is small enough, then the Julia set J(f
λ
) of f
λ
is a Cantor set of circles. In this paper we show that the Hausdorff dimension of J(f
λ
) has the following asymptotic behavior
dim
H
J
(
f
λ
)
=
1
+
log
2
log
p
+
O
(
|
λ
|
2
−
4
/
p
)
,
as
λ
→
0
.
An explicit error estimation of the remainder is also obtained. We also observe a ‘dimension paradox’ for the Julia set of Cantor set of circles.