These data consist of quantitative and categorical scores for phenotypic attributes of 88 types of galls induced on oak trees (Quercus spp.) by cynipid gallwasps (Hymenoptera: Cynipidae: Cynipini). The recorded variables focus on attributes such as hardness, presence of surface spines or coatings of sticky resin, each of which are thought to contribute to protection of the gall inhabitants form attack by natural enemies such as parasitoid wasps and birds. Cynipid galls have separate sexual and asexual generation galls, each with different phenotypes. The dataset comprises values for 31 sexual generation galls and 58 asexual generation galls of a total of 69 cynipid species. The biological rationale for regarding these phenotypic traits as defences is explained in Bailey et al (2009). The purpose of these data is to include them as explanatory variables in statistical analyses that seek to quantify the effects of gall traits on the composition and abundance of parasitoid natural enemies in cynipid gall communities. Full details about this dataset can be found at https://doi.org/10.5285/bc10f720-2bb6-4ff4-ad63-257663fd41a3