Insecticides are used across the world as it is evaluated that poses a risk to aquatic life especially fish, which are very sensitive in response to change in environmental conditions. The current study evaluated the effects of bifenthrin on Ctenopharyngodon idella's behavioral and hematology alterations. The acute toxicity 96-hr LC 50 of bifenthrin for grass carp was determined as 6.5µg/L. Fish were divided into four groups i.e., one control and three experimental groups having eight fish in each group. Control group was not exposed to bifenthrin. Experimental fish were exposed to sublethal (1/3 rd of LC 50 ) doses of bifenthrin i.e., 2.16 µg/L for 30 days. Behavioral parameters of C. idella were observed at acute as well as sub-lethal concentrations. It was observed that behavioral parameters of C. idella such as opercular movement, somersaulting activity, convulsions rate, air gulfing was significantly (p<0.05) increased by increasing the bifenthrin concentration. Fin movements and swimming rate was also increased with increase in bifenthrin concentration but at later stage fish became motionless and sluggish. Body color was changed from grey to pale and gills from bright to light red color as bifenthrin concentration increased. Blood parameters such as red blood cell counts (RBCs), White blood cell counts (WBCs), Hematocrit (Hct), Hemoglobin (Hb), Mean corpuscular hemoglobin (MCH), Mean Corpuscular Hemoglobin Concentration (MCHC) were measured at sub lethal exposure of bifenthrin after 15 and 30 days. The findings revealed that RBCs, Hb, Hct, PCV and MCHC were decreased significantly (p<0.05) and WBCs, MCV and MCH were increased significantly (p<0.05) after bifenthrin exposure. It was concluded that bifenthrin has potential to disturb the behavior and to alter the hematological profile of C. idella. The aim of present study is to explore the toxicity of insecticides.