Two new alkaloids with the β-carboline skeleton, pyridindolols K1 (C18H18N2O5) and K2 (C16H16N2O4), were isolated from the culture broth of Streptomyces sp. K93-0711. The structure of pyridindolols were established by spectroscopic investigations and chemical transformations. Pyridindolol K2 inhibited the adhesion of HL-60 cells to LPS-activated HUVEC monolayer (IC50 = 75μg/ml).