We consider the modified q -analogue of Riemann zeta function which is defined by ζ q ( s ) = ∑ n = 1 ∞ ( q n ( s − 1 ) / [ n ] s ) , 0 < q < 1 , s ∈ ℂ . In this paper, we give q -Bernoulli numbers which can be viewed as interpolation of the above q -analogue of Riemann zeta function at negative integers in the same way that Riemann zeta function interpolates Bernoulli numbers at negative integers. Also, we will treat some identities of q -Bernoulli numbers using nonarchimedean q -integration.