2-FAL (2-furaldehyde) and 5HMF (5-(hydroxymethyl-furfural) are two main by-products of the thermal degradation of cellulose paper insulation of power transformers’ windings. The detection of these compounds in the insulating oil of transformers is essential to investigate the ageing of the oil-paper system in order to avoid failures. To this aim a non-conventional surface plasmon resonance (SPR) platform in plastic optical fiber (POF) has been proposed by our group for the detection of 2-FAL in transformer oil. Besides a biomimetic receptor has been introduced, i.e. a molecularly imprinted polymer (MIP), which gives a noticeable selectivity to the device and many advantages with respect to the biological counterparts. Here the study has been extended to the very similar compound 5-HMF, in order to better establish the selectivity of the device in the particular oil matrix considered. To this aim the analysis of the binding interactions of two furanic compounds with the molecularly imprinted polymer (MIP) has been performed. The high sensitivity and the low amount of binding MIP material required for the investigation are two advantageous aspects of the SPR method to investigate the interactions of 2-FAL and 5-HMF with MIPs. Tests have been carried out on the same SPR-MIP sensor exposed to different 5-HMF and 2-FAL concentrations in the insulating oil by recording the plasmon resonance wavelength shift with the concentration of the furanic compounds. The results show that the 2-FAL has a higher affinity than 5-HMF for the specific MIP, demonstrating the good selectivity of the MIP receptor even in the very complex matrix considered.