PMMA flames are used as surrogate fuels for fire studies. Horizontal slab PMMA flame is studied here in laminar conditions. In particular, the CH radical field is obtained in a qualitative manner with respect to the luminous flame. CH-PLIF was used to obtain the CH radical field, along with simultaneous imaging of the flame luminosity. This was done at various time instances after ignition, and the change in flame shape and the CH field was observed. It was found that CH field was present in the same zone as the luminous flame. Since the luminosity is due to black body emission from the soot, it can be seen that the CH radicals exist in the same region as the soot region in the PMMA flames. This information along with OH radical field information will be useful for validating computational models for fire prediction. © 2021, Springer Nature Singapore Pte Ltd.