We report on the first ever use of nondestructive micrometer-scale synchrotron-computed microtomography (CMT) for biochar material characterization as a function of pyrolysis temperature. This innovative approach demonstrated an increase in micron-sized marcropore fraction of the cotton hull (CH) sample, resulting in up to 29% sample porosity. We have also found that initial porosity development occurred at low temperatures (below 350 degrees C) of pyrolysis, consistent with chemical composition of CH. This innovative technique can be highly complementary to traditional BET measurements, considering that Barrett-Joyner-Halenda (BJH) analysis of pore size distribution cannot detect these macropores. Such information can be of substantial relevance to environmental applications, given that water retention by biochars added to soils is controlled by macropore characteristic among the other factors. Complementing our data with SEM, EDX, and XRF characterization techniques allowed us to develop a better understanding of evolution of biochar properties during its production, such presence of metals and initial morphological features of biochar before pyrolysis. These results have significant implications for using biochar as a soil additive and for clarifying the mechanisms of biofuel production by pyrolysis.