Blaps rynchopetera Fairmaire with the extensive pharmacological activities is a medicinal insect. In the present study, a GC-MS method combined molecular docking was developed for exploring the active component in the low-polarity extract against α-amylase from Blaps rynchopetera. As a result, 20 compounds were identified in this extract by GC-MS. Among them, although the relative content of 9,12-octadecadienoic acid (Z, Z)- was the highest, its binding energy was significantly higher than that of pentadecanoic acid (−4.11 kcal/mol) with the relative content of 0.03%. Pentadecanoic acid was completely wrapped in the active site of α-amylase and interacted with amino acid residues Trp 58, Trp 59, Tyr 62, Gln 63, His 101, Leu 162, Leu 165, Asp 197, Ala 198, Ser 199, Lys 200, His 201, Glu 233, Val 234, Ile 235, Asp 300 and His 305 through the van der Waals forces and electrostatic forces. The results indicated that pentadecanoic acid possessed the α-amylase inhibitory activity and it was the potential hypoglycemic component in the low-polarity extract of Blaps rynchopetera Fairmaire. [ABSTRACT FROM AUTHOR]