Abstract: The invention provides tennis balls which comply in their behavior with the requirements of the "Rules of the International Lawn Federation" and which consist wholly or partially of a rubber based on natural and/or synthetic rubber which contains 15 to 50 parts by weight of a finely powdered aminoplast resin with a specific surface area of >5m.sup.2 /g. Suitable fillers for the rubber are urea/formaldehyde and melamine/formaldehyde polycondensation products. The tennis balls according to the invention can either have an internal gas pressure of 1.4 to 2.3 kg/cm.sup.2 (absolute) or they can be non-inflated, i.e. internally they have atmospheric pressure. The good behavior of these tennis balls is retained over an extended period of play. The tennis balls according to the invention are either provided with a textile or felt covering or they have no covering.