Abstract: In order to meet the need of establishing a standard haematological profile for fish pathological purpose, altogether 741 healthy fingerlings of grass carp (Ctenopharyngodon idellus) were examined during September, 1979-August, 1980. Results including 9 haematological parameters, their monthly variations and factors that affect the estimates are given in the present paper.The year-round means of 9 heamatological parameters of the fingerlings were: red blood cell (RBC)—2.32±0.47 106mm3, haemoglobin (Hb)—6.34±1.08 g%, haematocrit (Ht)—26.83±4.89%, mean cell volume (MCV)—119.38±24.20 μ3, mean cell haemoglobin (MCH)—27.73±5.24 pg, mean cell haemoglobin concentration (MCHC)—24.02± 4.44%, erythrocyte sedimentation rate (BSE)—2.49±0.92 mm/hr, plasma total protein—2.99±0.53g%, plasma glucose concentration—115.42±31.01mg%. The reliability of all parameters except ESR and plasma glucose concentration are approximately identical, with C. V. around 20%.There was a monthly fluctuation in fish haematological parameters, of which the higher values occurred in January, July and September. As to the factors that affect the parameters, the values of plasma total protein (PTP) was found to be correlated negatively with water temperature (t, in ℃) (r=-0.826, p=0.01), and the relationship may be described as YPTP=3.86-0.05t. On the other hand, values of Hb, Ht, MCV, MCHC and ESR were all found to be correlated significantly with fish body-weight (W, in g) and the regression formulae for respective haematological parameter may be given as: YHb = 4.84 + 0.039W, Y(Ht)=19.7 + 0.15W, YMcv = 88.77 + 0.62W, Y MChc = 22.25 + 0.133W, and YESR = 3.14 - 0.154W.