Y3Ba5Cu8O18 (Y-358) and Y3Ba5Ca2Cu8O18 (YCa-358) compounds were prepared by the so-called sol gel method. The effect of doping Ca atoms into the Y3Ba5Cu8O18 superconductor is studied by employing the electrical resistivity measurements at various magnetic fields. The possible degradation in microstructural and superconducting properties due to the addition of Ca was discussed. The resistivity as a function of. temperature measurements shows that the depression in superconducting temperature is more pronounced for both samples. A systematic analysis of the magnetoresistivity of the Y-358 and YCa-358 compounds has been carried out by using the thermally activated flux flow (TAFF) model. The TAFF activation energy, U, is field dependent and obeys the power law U= cH(-alpha), where alpha increases while c decreases with the addition of Ca. Furthermore, U and the calculated upper critical field, H-c2, decrease with the addition of Ca.