Rationale: The fundamental understanding of Grignard-type organolanthanides(III) is still in its infancy. Decarboxylation of metal carboxylate ions is a powerful method to obtain organometallic ions which are well suited for gas-phase investigation by using ESI-MS in combination with DFT calculations. Methods： (RCO2)LnCl3- (R = CH3, Ln = La-Lu except Pm; Ln = La, R = CH3CH2, CH2CH, CHC, C6H5 and C6H11) ions were produced via ESI of LnCl3 and RCO2H/RCO2Na in methanol. Collision-induced dissociation (CID) was employed to examine whether RLnCl3- can be obtained via decarboxylation of (RCO2)LnCl3-. With the aid of DFT calculations, the influences of Ln and R on the formation of RLnCl3- can be uncovered. Results: When R was fixed as methyl, CID of (CH3CO2)LnCl3- (Ln = La-Lu except Pm) all gave (CH3)LnCl3- and LnCl3·- with a variation in the relative intensity ratio of (CH3)LnCl3-/LnCl3·-. The trend is following as (CH3)EuCl3-/EuCl3·- < (CH3)YbCl3-/YbCl3·- ≈ (CH3)SmCl3-/SmCl3·- < other (CH3)LnCl3-/LnCl3·-, which generally complies with the trend of Ln(III)/Ln(II) reduction potentials. When Ln was fixed as La and R groups were varied as CH3CH2, CH2CH, CHC, C6H5 and C6H11, the fragmentation behaviors of these (RCO2)LaCl3- are diverse. Except for (C6H11CO2)LaCl3-, the rest four (RCO2)LaCl3- ions all underwent decarboxylation to give RLaCl3-. The relative intensities of RLaCl3- compared to (RCO2)LaCl3- decrease as follow: CHC > CH2CH > C6H5 > CH3 > CH3CH2 >> C6H11 (not visible). Conclusion： A series of Grignard-type organolanthanide(III) ions RLnCl3- (R = CH3, Ln = La-Lu except Pm; Ln = La, R = CH3CH2, CH2CH, CHC and C6H5) were generated from (RCO2)LnCl3- via CO2 loss while (C6H5)LaCl3- not. The experimental and theoretical results suggest that the reduction potentials of Ln(III)/Ln(II) couples as well as the bulkiness and hybridization of hydrocarbyl groups play crucial roles in promoting or limiting the formation of RLnCl3- via decarboxylation.