Objective: To compare the vaginal cytology of ovulating and non-ovulating queens. Procedure: The study group comprised 15 queens showing behavioural oestrus. Ovulation was induced in 7 (dioestrus group) and 8 were left untreated (postoestrus group). Vaginal smears were collected from all animals prior to ovariohysterectomy on day 7. Epithelial cells were classified as basal-parabasal, intermediate, superficial, or anucleated superficial cells and counted using computer-assisted image analysis. From each smear, 50 representative vaginal epithelial cells were chosen. Digital images of cells were taken and cell area, cytoplasm area, nucleus area, cell diameter, cell perimeter, nucleus/cytoplasm ratio and red-green-blue (RGB) values were measured using image analysis software. Measurement data were compared between groups. Results: Ovulation induction was successful in all animals. The swabbing procedure in oestrus did not induce ovulation in any postoestrus queens. Mean duration of oestrus was 6.65 ± 0.44 and 4.71 ± 0.32 days (P > 0.05) in the postoestrus and dioestrus queens, respectively. Intermediate cell count averaged 21.43% in dioestrus cats and 10.76% in postoestrus cats (P < 0.05). Epithelial cells in the postoestrus group had higher cell area, cytoplasm area, cell diameter and cell perimeter measurements (P < 0.01). Red (90.9 ± 1.6), green (76.1 ± 1.3) and blue (83.6 ± 1.4) channel values in postoestrus were higher than the values (81.3 ± 0.8, 65.8 ± 0.9 and 74.0 ± 0.7, respectively) in dioestrus (P < 0.01). Conclusion: Induction of ovulation in oestrus queens results in a significant increase in the number of intermediate cells and a significant decrease in both the dimensions and RGB values of vaginal epithelial cells on day 7. © 2014 Australian Veterinary Association.