Li-NMR chemical shifts were studied on adsorbed lithium ions in strongly acidic cation exchange resins with different degrees of crosslinking. The observed chemical shifts measured from the reference peak of butyl lithium have shown a linear relation with crosslinking degrees, regardless the types of gel or porous resins. Li-NMR chemical shifts, relating to the chemical conditions of the adsorbed lithium ion, directly indicate the microscopic environment of the ion exchange sites where cations are accommodated. Thus Li-NMR can be used as a convenient tool to analyze the crosslinking degrees or mobility of cations in the cation exchange resins.