Polycrystalline samples of Ca1−xBixMn1−ySiyO3−δ (x = y = 0.00, 0.02, 0.03, 0.04, and 0.05) are prepared by conventional solid state reactions. Thermoelectric properties are measured at 300–700 K. All the samples are single phase with an orthorhombic structure. Thermopower of all the samples is negative, indicating that predominant carriers are electrons over the entire temperature range. Among the samples, Ca0.98Bi0.02Mn0.98Si0.02O3−δ has the highest dimensionless figure of merit ZT = 0.02. This value represents an improvement of about 162% with respect to the parent compound of CaMnO3−δ at 300 K.