Abstract The electrical resistivity ρ(T) versus temperature data of as-prepared and O2-annealed Cu0.5Tl0.5Ba2(Ca2−yMgy)(Cu0.5Zn2.5)O10−δ (y=0, 0.5, 1.0) samples is analyzed for fluctuations induced conductivity analysis in the temperature regime well above the critical temperature. The analysis has been carried out employing Aslamazov and Larkin (AL) and Lawrence and Doniach (LD) models. The coherence length, inter-planar coupling, exponent and dimensionality of fluctuations are determined from this analysis. It has been observed in as-prepared and oxygen post-annealed samples that the crossover temperature associated with two distinct exponents and the excess conductivity data fits very well with the two-dimensional (2D) and three-dimensional (3D) AL equations. The cross-over temperature To is shifted to lower temperatures with enhanced Mg doping. The width of 3D AL region is reduced with increased Mg doping, however, some improvement is observed after post-annealing in the oxygen atmosphere. Moreover, a decrease in the coherence length along the c-axis is observed with the doping of Mg in the final compound. We have elucidated from these analyses that higher thallium contents in the final compound promote a decrease in the density of mobile carriers in CuO2 planes, which suppresses the coherence length along the c-axis and superconductivity parameters.