Abstract This paper presents a state estimation structure for a Continuous Stirred Tank Reactor (CSTR), by means of an Asymptotic Observer jointly with a disturbance high order sliding mode-based estimator. The proposed estimation scheme allows the asymptotic reconstruction of the concentration inside the reactor based on the measures of the temperature inside the reactor and the temperature inside the jacket, in presence of changes in the global coefficient of heat transfer <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mi>U</m:mi> <m:mi>A</m:mi> </m:math> $UA$ , the Arrhenius constant <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msub> <m:mi>k</m:mi> <m:mn>0</m:mn> </m:msub> </m:mrow> </m:math> ${k_0}$ and the activation energy E . Additionally, the structure is able to estimate <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mi>U</m:mi> <m:mi>A</m:mi> </m:math> $UA$ and the kinetics term <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msub> <m:mi>k</m:mi> <m:mn>0</m:mn> </m:msub> </m:mrow> <m:mrow> <m:msup> <m:mi>e</m:mi> <m:mrow> <m:mo>−</m:mo> <m:mrow> <m:mfrac> <m:mi>E</m:mi> <m:mrow> <m:mi>R</m:mi> <m:mi>T</m:mi> </m:mrow> </m:mfrac> </m:mrow> </m:mrow> </m:msup> </m:mrow> </m:math> ${k_0}{e^{- {E \over {RT}}}}$ . The properties of the proposed scheme are proved mathematically and verified through numerical simulations.