An anti-bacterial water absorbing agent having excellent water absorption, anti-bacterial activity, and powder flow properties. The agent is useful in the manufacture of absorbent materials particularly for absorbing urine, blood, and body fluids and the like. The agent comprises a water absorbing resin (A) having pendant acid groups, at least on acid group being in the form of a quaternary ammonium salt having the general formula (1). ##STR1## wherein --X.sup.- is an anionic pendant group covalently bonded to backbone in the water absorbing resin (A) and R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are organic groups. In embodiments, at least one of the organic groups on the ammonium ion is an aliphatic alkyl group having 5 to 20 carbons. At least one of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is a C.sub.5 to C.sub.20 aliphatic alkyl group. The resin has a quaternary nitrogen atom content of about 2.times.10.sup.-4 % to about 0.8% by weight.