MicroRNAs (miRNAs) are an abundant class of approximately 22-nucleotide (nt)-short noncoding RNA molecules present in the genomes of all multicellular organisms that act through base pairing to partially complementary sequences of the 3'untranslated region (UTR) of targeted mRNAs. Using bioinformatic approach, we found that the 3'UTR of the Fibroin L chain (Fib-L) mRNA matches perfectly the nucleotides 2-8 at the 5' end of the miRNA-965 and miRNA-1926. These two miRNAs might act as regulators of Fib-L gene expression at the post-transcriptional level. To examine whether Fib-L is directly targeted by miRNA-965 and miRNA-1926 in vitro, miRNA expression vectors and target reporter vector with 3'UTR of Fib-L were constructed respectively. Two vectors were co-transfected into Sf21cells. The luciferase assay showed that miRNA-965 and miRNA-1926 may down regulate the expression of Fib-L via complementary interaction with the target sites in 3'UTR.