Objective: We aimed at exploring predictors of improvement in clinical and functional outcomes of patients on clozapine with chronic treatment-resistant schizophrenia admitted into rehabilitation wards. Method In a cross-sectional study of 62 patients on clozapine augmented with oral and parenteral antipsychotics, predictors of HoNOS (Health of the Nation Outcome Scales) scores were analysed using ordinal logistic regression. Result: Augmentation with parenteral antipsychotics was associated with lower psychotic symptom scores (OR 0.38 [95%CI 0.15, 0.99]) and activity of daily living scores (OR 0.36 [95%CI, 0.13, 0.96]) compared with oral antipsychotics. Increased age was a predictor of behavioural disturbances, physical illness and cognitive problems for all clozapine patients, and female gender was associated with the increase in depression scores. Conclusion: The addition of parental antipsychotics to clozapine in patients with treatment-resistant schizophrenia might have potential benefits for clinical and functional outcomes and needs a further investigation.