The aim of this study is to evaluate the effect of movement and deformation of red blood cells on therapeutic nanoparticle delivery to tumor tissue through the pores on its vasculature wall. For this purpose, nanoparticle-blood flow through a segment of tumor microvascular is numerically studied. Blood is modeled as a mixture of plasma as a continuous fluid and red blood cell as an elastic solid by using coupled fluid structure interaction method. Lagrangian approach is used for tracking nanoparticles in the tumor microvessel, and effective forces from the fluid are applied to the particles. The effect of pore size and tumor interstitial fluid pressure on the deformation of red blood cell in the vicinity of the pore and on the particle delivery is studied. It is shown that by increasing the pore size and decreasing the interstitial fluid pressure, the amount of deformation of the cell and nanoparticle delivery are increased. The effect of transient motion and deformation of red blood cells on the amount of particles delivered to the tumor is investigated and it is shown that by approaching the cell to the pore, the particle delivery initially increases and then decreases. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.