The present study was conducted to investigate the effects of parasite infection on haematological parameters of common carp, Cyprinus carpio. To this end, fish with same age were sampled from a warm water fish farm. After fish sampling, fish were transferred to lab for parasite study. Parasite incidence percent and density were calculated for two population carps. After parasite study, to investigate the haematological parameters, the blood sampling was carried out from two group fish i.e. infected (n = 20) and non-infected fish (n = 20). According our results, totally three parasite species were identified including Dactylogyrus sp., Trichodina sp. and Lernaea cyprinacea. Significant differences were observed between infected and non-infected fish (P \ 0.05). In this regard, the values of haematocrit, haemoglobin and red blood cell were lower in infected fish than healthy individuals (P \ 0.05). In contrast, number of white blood cells (WBCs) were higher in infected fish compared to noninfected fish (P \ 0.05). In conclusion, our study reveals that the parasite infection was responsible for altering the haematology of common carp. Increased number of WBC may be in relation to the defense mechanism and immunological responses against parasites.