Aim To explore effects of lipoprotein(a) [Lp(a)] containing immune complexes (IC) on matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinase-1 (TIMP-1) gene expression in U937 cells. Methods U937 cells were incubated with native, oxidized Lp(a) or Lp(a)-IC, respectively. mRNA expression of MMP-1 and TIMP-1 in U937 cells were measured by reverse transcriptase polymerase chain reaction (PT-PCR). Results Normal U937 cells lowly expressed MMP-1 (0.076±0.012), but highly expressed TIMP-1(0.973±0.031). The expression of MMP-1 mRNA induced by nature, oxidized Lp(a), and nature, oxidized Lp(a)-IC were 0.361±0.016, 0.330±0.019, 0.106±0.006 and 0.089±0.008, respectively, while the expression of TIMP-1 mRNA were 0.229±0.017, 0.360±0.018, 0.157±0.025 and 0.967±0.031, respectively. Nature Lp(a) had no effect on expression of MMP-1and TIMP-1 mRNA. Oxidized Lp(a) can induce slightly expression of MMP-1 and markedly down-regulate expression of TIMP-1. Similarly, nature and oxidized Lp(a)-IC had significantly more effect on mRNA expression of MMP-1 and TIMP-1 than control (P<0.001). Moreover, their effect on MMP-1 and TIMP-1 expression changed in a dose-dependent manner. Conclusion Lp(a)-IC stimulates the expression of MMP-1 mRNA and down-regulates the expression of TIMP-1 mRNA in U937 cells.