The spectral and quantum-chemical studies of phosphonium ylides derivatives of 2-oxazoline-5-one with both conjugated and non-conjugated substituents were performed. It was found that considerable positive charge is located at phosphorus atom, whereas the substantial negative charge is fixed at sulphur atom. It has been found from the calculations and 13C NMR spectral data that introducing of the non-conjugated and conjugated substituents in the position 2 of the oxazole cycle in thiaphosphonium ylides causes only small change in the molecular equilibrium geometry and in charge distribution in oxazole moiety, whereas spectral characteristics of substituted derivatives are very sensitive to the nature of the lowest electron transitions which reflects in changes of their absorption maxima.