An oxygen sensor bung of motor vehicle exhaust pipe comprises at least a base, a catalytic converter and a seal lid. The base has an external connection section at one end that contains a first chamber to hold the catalytic converter and is fastened by the seal lid. The external connection section has a first external thread on the surface to fasten to a holding seat of an exhaust pipe. The base has a second chamber on another end with a third internal screw hole formed inside to hold an oxygen sensor by fastening with a second external thread formed thereon. The catalytic converter includes a barrel type casing containing a beehive structure made of precious metal to increase exhaust gas process area. Therefore impurities in the exhaust gas can be reduced and timely replacement of the catalytic converter can be accomplished, and accurate detection of oxygen content can be achieved.