The extract of green peel of Juglans mandshurica Maxim was extracted by common method for studying its insecticidal activities and analyzing the active components. Results showed that the alcohol extract and the chloroform part of extract (separated with chloroform from alcohol extract) form green peel of J. mandshurica have insecticidal activities in contact toxicity and stomach toxicity against larvae of Lymantria dispar L.. After application of the extracts for five days, the corrected mortality of larvae of Lymantria dispar for both extracts was more than 50% in contact toxicity and stomach toxicity at the concentration of ≥ 5 g·L~(-1). The insecticidal activity for both alcohol extract and chloroform part of extract is more effect in contact toxicity than in stomach toxicity, but no significant difference in the insecticidal activities was found between alcohol extract and chloroform part of extract. The active components in the chloroform part of extract from green peel of J. mandshurica were analyzed by GC-MS. The analyzed results showed that the active components in the chloroform part of extract are: (1) juglone (5-hydroxy-1,4-naphthaoquinone), the relative content 27.11%, (2) 1,5-Naphthalenediol, the relative content 9.52%, (3) 7-Methoxy-1-tetralone, the relative content 6.81%, (4) Benzofuran, 2,3-dihydro-, the relative content 6.76%, (5) 4-Hydroxy-2-methoxycinnamaldehyde, the relative content 3.99%, (6) 2-Methoxy-4-vinylphenol, the relative content 3.05%. The extract of green peel of Juglans mandshurica Maxim was extracted by common method for studying its insecticidal activities and analyzing the active components. Results showed that the alcohol extract and the chloroform part of extract (separated with chloroform from alcohol extract) form green peel of J mandshurica have insecticidal activities in contact toxicity and stomach toxicity against larvae of Lymantria dispar L .. After application of the extracts for five days, the corrected mortality of larvae of Lymantria dispar for both extracts was more than 50% in contact toxicity and stomach toxicity at the concentration of ≥ 5 g · L -1. The insecticidal activity for both alcohol extract and chloroform part of extract is more effect in contact toxicity than in stomach toxicity, but no significant difference in the insecticidal activities was found between alcohol extract and chloroform part of extract. The active components in the chloroform part of extract from green peel of J. The analyzed results showed that the active components in the chloroform part of extract are: (1) juglone (5-hydroxy-1,4-naphthaoquinone), the relative content 27.11%, (2) 1 , The relative content of 9.52%, (3) 7-Methoxy-1-tetralone, the relative content of 6.81%, (4) Benzofuran, 2,3- dihydro- the relative content of 6.76% -Hydroxy-2-methoxycinnamaldehyde, the relative content of 3.99%, (6) 2-Methoxy-4-vinylphenol, the relative content of 3.05%.