The effects of the spark plasma sintering (SPS) parameters, such as heating rate , temperature T and soak time t(s), and impurities on in-line transmission T-in were examined in MgAl2O4 spinel. The SPS processing at T=1300 degrees C for t(s)=20min with a low heating rate of =10 degrees C/min is a preferable condition for attaining higher T-in. For the higher T or the longer t(s), grain coarsening enhanced the coalescence of residual pores and second phase precipitation, resulting to the limited T-in even at the slow . Although the lower T and longer t(s) attained fine and dense microstructure simultaneously, the maximum T-in was limited to about 50%. The limited transmission, particularly in the visible range, can be ascribed to the discoloration caused by the carbon contamination. The carbon contamination arose from the preexisting trace CO3 impurities, irrespective of the SPS conditions. For the higher , which is the primary advantage of the SPS technique, the additional carbon contamination occurred from the paper/die and remained as glassy carbon in the matrix. To attain higher T-in by the SPS technique, the lower and T, and the shorter t(s) should be utilized after removing the impurities.