An experimental study of xylene isomers interconversion (isomerization) kinetics was conducted to gain a deeper insight into the field. Two beta zeolites with SiO2/Al2O3 ratio of 35 (BEA35) and 38 (BEA38) were used as catalysts for the performed experiments. The isomerization reactions were carried out under the following conditions: 513, 493, 473, and 453 K at 2.1 MPa in liquid phase. It was verified that all reactions were in the kinetic-controlled regime. Kinetic constants were estimated with four different models; two of them were based on the xylene isomerization thermodynamic equilibrium from the literature. The linear reaction scheme, which does not consider the direct conversion between p- and o-xylene, presented a better fit to the experimental values. Higher conversion of p-xylene was observed when compared with the conversion of the other two isomers. This may be attributed to its smaller molecular size. BEA35 presented better performance due to its higher amount of Brønsted acid sites. Finally, activation energies over the two catalysts, estimated through Arrhenius equation, presented similar values. This work was financially supported by Project POCI-01-0145-FEDER-006984—Associate Laboratory LSRE-LCM funded by FEDER through COMPETE2020 Programa Operacional Competitividade e Internacionalização (POCI)—and by national funds through FCT—Fundação para a Ciência e Tecnologia. This work was financed by AIProcMat@N2020, NORTE-01-0145-FEDER-000006. Ms. Shi Qian acknowledges the financial support from China Scholarship Council for her Ph.D. grant (File No. 201505130003, 2015-2019). Dr. M.G. Plaza acknowledges the award of a Ramon y Cajal contract (RyC-2015-17516) from the Spanish MINECO. The support of Prof. M.F. Ribeiro and Dr. A.R. Fernandes on the pyridine desorption by FTIR is highly appreciated. The authors thank Clariant Produkte (Deutschland) GmbH for providing the beta SAR = 35 zeolite and give special thanks to Dr. Ernst Köhler. Peer reviewed