<p>Studying how habitat conversion influences morphology is essential for predicting long-term viability of insect populations. However, there is limited knowledge of how the morphology of aquatic insects (such as Odonata) varies among habitat types in fragmented landscapes such as subtropical forests in the Neotropical Region. Here, we test for shape differences in the neotropical dragonfly <i>Erythrodiplax castanea</i> (Burmeister, 1839) (Odonata, Libellulidae) inhabiting native and planted forest habitats in the southern Brazilian Atlantic Rainforest. Specifically, we compared linear morphometric measurements in adult dragonflies found in patches of mixed ombrophilous forests and tree plantations. We measured eight traits (abdominal length, thorax width, fore- and hindwing length and width, fore- and hindwing area and aspect ratio) and used analysis of covariance (with body length as covariate to account for size) to assess variation in each trait between forest types. Models showed that specimens with similar sizes (body lengths) had significant larger values of thorax width, forewing length and aspect ratio in tree plantations than in mixed ombrophilous forest. Shape differences in adult dragonflies are likely explained by the differences in microclimate (insolation, temperature, humidity, wind) and habitat complexity (tree spacing) among mixed ombrophilous forest and tree plantations, suggesting that the processes driving adult odonate establishment differ between forest habitat types. We shed further light on how dragonfly morphology responds to changes in vegetation structure in the southern Atlantic Forest. Our findings can be useful to predict the effects of land cover conversion on dragonflies in South American subtropical forests.</p>