An exhaust gas sensor (100; 200) configured to detect an oxygen concentration or air-fuel ratio in exhaust gas, comprising: a sensor element that detects an oxygen concentration or air-fuel ratio; and a manganese reaction layer formed on at least part of a surface of the sensor element and formed of a substance containing an element capable of generating a complex oxide having manganese through reaction with a manganese oxide in the exhaust gas, wherein the exhaust gas sensor (100; 200) is configured to detect the oxygen concentration or air-fuel ratio in exhaust gas of an internal combustion engine that utilizes a fuel having a Mn concentration in excess of 20 ppm, the manganese reaction layer contains at least one element from among Zn, B, Ca, Ba, Sr, V and Y, as the element capable of generating a complex oxide having manganese, the exhaust gas sensor (100; 200) being characterized in that: at least part of the manganese reaction layer contains amorphous glass; a glass matrix that makes up the amorphous glass includes Si, B, Al, R and M as main constituents, wherein R is at least one element from among Li, Na and K, and wherein M is at least one element from among Zn, Ca, Ba, Sr, V and Y; mass ratios of main components, in terms of oxide, with an entirety of the glass matrix as 100 mass%, are: SiO 2 25 mass% to 40 mass%; B 2 O 3 20 mass% to 35 mass%; Al 2 O 3 1 mass% to 10 mass%; R 2 O 5 mass% to 20 mass%; M oxide 0 mass% to 25 mass%, and a total of the main components is 80 mass% or more. a sensor element that detects an oxygen concentration or air-fuel ratio; and a manganese reaction layer formed on at least part of a surface of the sensor element and formed of a substance containing an element capable of generating a complex oxide having manganese through reaction with a manganese oxide in the exhaust gas, wherein the exhaust gas sensor (100; 200) is configured to detect the oxygen concentration or air-fuel ratio in exhaust gas of an internal combustion engine that utilizes a fuel having a Mn concentration in excess of 20 ppm, the manganese reaction layer contains at least one element from among Zn, B, Ca, Ba, Sr, V and Y, as the element capable of generating a complex oxide having manganese, the exhaust gas sensor (100; 200) being characterized in that: at least part of the manganese reaction layer contains amorphous glass; a glass matrix that makes up the amorphous glass includes Si, B, Al, R and M as main constituents, wherein R is at least one element from among Li, Na and K, and wherein M is at least one element from among Zn, Ca, Ba, Sr, V and Y; mass ratios of main components, in terms of oxide, with an entirety of the glass matrix as 100 mass%, are: SiO 2 25 mass% to 40 mass%; B 2 O 3 20 mass% to 35 mass%; Al 2 O 3 1 mass% to 10 mass%; R 2 O 5 mass% to 20 mass%; M oxide 0 mass% to 25 mass%, and a total of the main components is 80 mass% or more. at least part of the manganese reaction layer contains amorphous glass; a glass matrix that makes up the amorphous glass includes Si, B, Al, R and M as main constituents, wherein R is at least one element from among Li, Na and K, and wherein M is at least one element from among Zn, Ca, Ba, Sr, V and Y; mass ratios of main components, in terms of oxide, with an entirety of the glass matrix as 100 mass%, are: SiO 2 25 mass% to 40 mass%; B 2 O 3 20 mass% to 35 mass%; Al 2 O 3 1 mass% to 10 mass%; R 2 O 5 mass% to 20 mass%; M oxide 0 mass% to 25 mass%, and SiO 2 25 mass% to 40 mass%; B 2 O 3 20 mass% to 35 mass%; Al 2 O 3 1 mass% to 10 mass%; R 2 O 5 mass% to 20 mass%; M oxide 0 mass% to 25 mass%, and a total of the main components is 80 mass% or more.