This study is conducted to examine the impacts of different rearing temperature and diet variation on haematological and serum biochemical parameters on the juvenile Lutjanus malabaricus, a commercially important fish species in were divided into eight treatments (4 temperatures × 2 diets) each with three replicates of five juveniles each. Fish were subjected to four different rearing temperatures (22, 26, 30 and 34°C) and fed with a commercial pellet and a natural shrimp diet. After 30 days of experimental period, blood samples were collected and transferred into two different tubes from each sample: One containing EDTA as an anticoagulant agent and the other without EDTA for serum collection. All the haematological and biochemical parameters in all the treatments were within the normal range. Changing temperature and diet led to a significant change (p<0.05) in the total length (TL), body weight (BW), red blood cell (RBC), haemoglobin (HB), haematocrit (HC), thrombocyte (TC) and white blood cell (WBC) but the change in mean corpuscular volume (MCV), mean cell haemoglobin (MCH) while mean cell haemoglobin concentration (MCHC) were not significant (p>0.05). The fish reared at 26°C and 30°C had significantly higher values than those reared at 22°C and 34°C (p<0.05). Total protein (TP), albumin (ALB), albumin/globin ration (A/G ratio), alkaline phosphatase (AP), aspartate aminotransferase (AST) and alanine transaminase (ALT) level were also significantly increased at 30°C and 26°C compared to that of 34°C and 22°C. Globulin (GLB) level showed the opposite trend. In all the cases the performances were higher in shrimp diet than pellet diet. It is suggested that these physiological parameters can be conveniently employed as health monitoring tools in fish culture practices. ABSTRAK Kajian ini dijalankan bagi meneliti impak perbezaan suhu dan variasi diet pada parameter hematologi dan serum biokimia pada juvenil Lutjanus malabaricus, satu spesies ikan komersial penting di Malaysia. Ikan (16-18 cm) dibahagikan kepada lapan rawatan (4 suhu × 2 diet) dan terdapat tiga replikat (5 ikan setiap replikat) bagi setiap rawatan. Ikan terdedah kepada empat suhu yang berbeza (22, 26, 30 dan 34°C) dan diberi makan pelet komersial dan diet udang semula jadi. Selepas 30 hari tempoh uji kaji, sampel darah diambil dan dipindahkan ke dalam dua tiub yang berbeza daripada setiap sampel: satu yang mengandungi EDTA sebagai agen antikoagulan dan yang lain tanpa EDTA untuk pengumpulan serum. Semua parameter hematologi dan biokimia dalam semua rawatan berada dalam julat normal. Perubahan suhu dan diet menyebabkan perubahan ketara (p <0.05) dalam jumlah panjang (TL), berat badan (BW), sel darah merah (RBC), hemoglobin (HB), hematokrit (HC), trombosit (TC) dan sel darah putih (WBC) tetapi perubahan jumlah min korpuskul (MCV), min sel hemoglobin (MCH), manakala nilai min kepekatan sel hemoglobin (MCHC) tidak signifikan (p > 0.05). Nilai yang lebih tinggi dilihat pada ikan yang diternak pada 26 dan 30°C daripada yang diternak pada 22 dan 34°C ...