We define S(n) the set of quadratic forms of rank n that are represented by a sum of squares. For a quadratic form f in S(n), we say f is a sum of k squares not divisible by p if there are integers a_｛ij｝＇s such that f(x_1, x_2, ..., x_n)=(a_｛11｝x_1+...+a_｛1n｝x_n)^2+...+(a_｛n1｝x_1+...+a_｛nn｝x_n)^2 and (a_｛i1｝a_｛i2｝ ... a_｛in｝,p)=1 for any i. We define s_p(n) the smallest integer t such that any f in S(n), f is a sum of at most t squares not divisible by p. In this talk, we consider the binary case, that is, we prove that s_2(2)=11, s_3(2)=7, s_5(2)=6 and 4 < s_p(2) < 8 for any p > 5.