The present study was undertaken to investigate the influence of tropical theileriosis on serum constituents, erythrocytes and platelets pictures and to study the correlation between the studied parameters. A total number of 26 cows were subjected to study. Out of them 16 cows were suffered from theileria infection. Comparing theileria infected group with the control group revealed significant decreases in total RBCS counts (p \ 0.01), haemoglobin concentration (p \ 0.01), packed cell volume (PCV) (p \ 0.01), platelets count (PLT) (p \ 0.01), plateletcrit (PCT) (p \ 0.01), significant decreases in serum total proteins (p \ 0.01), albumin (p \ 0.01), calcium (p \ 0.01), and phosphorus (p \ 0.01) levels, and significant increases in serum blood urea nitrogen (BUN) (p \ 0.05) and creatinine (p \ 0.05) levels, and in serum aspartate aminotransferase (p \ 0.01) and gamma glutamyl transferase (GGT) (p \ 0.01) activities. Correlations between serum biochemical parameters revealed significant positive correlations between total proteins and albumin (r = 0.598*), A/G ratio and albumin (r = 0.860**), calcium and albumin (r = 0.729*), calcium and A/G ratio (r = 0.752*), GGT and BUN (r = 0.539*), and significant negative correlations between A/G ratio and globulins (r = -0.809**) and between glucose and albumin (r = -0.614*). Erythrocytes count showed a significant negative correlation with mean corpuscular volume (MCV) (r = -0.966**) and red blood cells distribution width (RDW) (r = -0.909**). MCV showed a significant positive correlation with RDW (r = 0.860*) and PCV (r = 0.781*). RDW was positively correlated with PCV (r = 0.966**). PLT count showed a significant positive correlation with mean platelet volume (MPV) (r = 0.992**), platelets distribution width (PDW) (r = 0.956**) and PCT (r = 0.994**). Furthermore, MPV showed a significant positive correlation with PDW (r = 0.940**) and a negative correlation with PCT (r = -0.974**). PDW was negatively correlated with PCT (r = -0.974**). It could be concluded that theileria infection in cattle resulted in mia, thrombocytopenia, hypoproteinaemia, hypoalbuminaemia and hypophosphataemia, in addition to hepatic and kidney dysfunction.