Mechanical strain regulates the structure and mechanical properties of the engineering tissue. Previous studies showed that cyclic mechanical strain affect in development and function of cells in tissue formation on various three-dimension scaffolds. In this study, the effect of cyclic uniaxial tensile straining on cell morphology was investigated. The objective of this research is to investigate the effect of cyclic uniaxial strain on cells' growth on knitted PLGA (Poly-Lactide-co-glycolide) scaffolds. A biocompatible cyclic uniaxial tensile straining device (bioreactor) was developed. Cyclic uniaxial straining was applied at 1.8% strain for 4 hours daily. To study the effect of cyclic frequency on cells' growth, two sets (1Hz and 0.1 Hz) of frequencies were used. After two weeks stimulation, the cell morphology was studied with the aid of Hematoxylin & Eosin staining using paraffin sectioning. In both frequency sets the mean nuclei length are longer than unstrained specimens. The cell population also tended to orientate parallel to the straining axis. In 0.1Hz frequency straining, more cell population are aligned in the straining direction than in 1Hz frequency. This study has demonstrated that cyclic uniaxial strain affect on cell morphology and mechanical properties of engineering tissue.