Effects of Dy- substitution at rare earth site of recently identified giant magnetocaloric effect material Gd5Si2Ge2 on its crystal structure, magnetic and electronic transport properties have been studied. At room temperature, (DyxGd1-x)5Si2Ge2 (x = 0 - 0.8) compounds have monoclinic Gd5Si2Ge2 - type structure, but (DyxGd1-x)5Si2Ge2 (x = 0.9 - 1) have orthorhombic Sm5Ge4-type structure. The magnetic transition temperature (TC) decreases with increasing Dy- concentration. While the electrical resistivity (ρ) shows a marked decline at TC with metallic nature in the ordered state and becomes more resistive in Dy- rich side. Thermoelectric power (S) undergoes a slope change at TC and the signature of phonon drag effects at low temperature is seen for alloys with lesser Dy- concentration and end members.