Purpose -The purpose of this paper is to study the microwave interactions in polymer thick film resistors, namely, polyvinyl chloride (PVC)-graphite thick film resistors, and its applications in trimming of these resistors. Design/methodology/approach -We applied microwave radiation in the form of pulses of various pulse durations and with different powers to polymer thick film resistors and observed the variation of resistance of these resistors with microwave radiation. Findings -The paper finds that microwave radiation can be used for trimming of polymer thick film resistors. Research limitations/implications -The research implication of this paper is that polymer thick film resistors can be trimmed practically using this method. Practical implications -The practical implication of this paper is that we can trim the polymer thick film resistors, namely, PVC-graphite thick film resistor, by using this method. Originality/value -The value of the paper is in showing that microwave radiation can be used to trim downwards in the case of high-value resistors and trim upwards in the case of low-value resistors.