Clopyralid is a selective, auxins type herbicide of pyridine carboxylic acid group which is used in the cultivation of vegetables for the control of broad leaf weeds of the family polygonaceae, compositae, legmuminosae and umbelliferae in sugarbeet, fodder beet, oilseed rape, brassica, onions, leeks strawberries, flax and grassland. About 8,91,662 lbs active ingredient of clopyralid was used in the US. Clopyralid can be consider as a safe herbicide for mammals as its LD50 for rat is 3738 (for male) and 2675 mg/kg (for female) but it could be harmful for the aquatic life for example rainbow trout and bluegill sunfish have the LD50 values 103.5 and 125.4 mg/kg repectively. study pertaining to its persistence behavior in soil is essential to get an idea about its extent of residue thereby predicting the risk of residual toxicity and ground water pollution. The work presented in this monograph have been submitted as a thesis for partial fulfillment of the M.Sc. degree program to G. B. Pant University of Agriculture & Technology, Pantnagar 263 145, (Uttarakhand), India under the guidance of Dr. N. K. Sand, Dr. Sudha Kanaujia, Dr. Anjana Srivastava and Dr. Shishir Tandon.