Background: Functional constipation is a common disorder in children, and evidence suggests that psychiatric disorders may induce functional constipation in children. The present study aimed to evaluate and compared anxiety disorders in children with and without functional constipation. Methods: This case-control study was conducted on 200 children (100 cases with functional constipation and 100 children without functional constipation) aged 15 - 8 years. The participants’ age and gender were evaluated and compared in two groups. Moreover, the Spence Children Anxiety Scale (SCAS) (parent form) for children was completed. Finally, the collected data were analyzed using SPSS software version 24. Results: Of 200 evaluated cases in the case and control groups, there were 46 (46.0%) and 59 (59.0%) males, respectively (P = 0.113). The mean ± SD of age in total, the case, and the control groups were 7.51 ± 1.91, 7.61 ± 0.91, and 7.41 ± 2.49 years, respectively (P = 0.585). Furthermore, SCAS in the case group was significantly higher (33.06 ± 14.4 vs. 24.8 ± 14.9, P = 0.001). Furthermore, the mean of separation anxiety disorder (P = 0.001), generalized anxiety (P = 0.003), and obsessive-compulsive disorder (OCD) were significantly higher in the functional constipation group (P = 0.001). Conclusions: Anxiety was higher in children with functional constipation than in children without functional constipation (ie, control group), among which separation anxiety, generalised anxiety, and OCD were significantly different in the two groups.