A radiocarbon (14C) activity analysis in the tree rings around Ignalina nuclear power plant (INPP) has been carried out with the aim to test the hypothesis to use 14C tree-ring analysis data as a tool for the reconstruction of gaseous releases from NPP to the environment. The INPP has been in decommissioning state since the end of 2009. Tree-ring samples for 14C analysis were collected 7 yr after final power unit shutdown from the INPP vicinity. The samples from 5 sampling locations were collected, prepared and measured using the Single Stage Accelerator Mass Spectrometer (SSAMS). Data analysis represents observable Ignalina NPP influence by 14C increase up to 15 pMC (percent modern carbon) in tree rings. Good correlations of the 14C concentrations and wind direction were obtained. The main purpose of this article was to match 14C measurement data along with the atmospheric dispersion modeling of emissions in order to retrospectively characterize the emission source.