Salesforce1 doesn't support custom buttons, but you might consider moving that button's functionality to a Publisher Action, which is supported in both the web GUI and in Salesforce1. (This is assuming your custom button is a detail button.)
Publisher Actions are clearly SFDC's preferred method for adding capabilities to a record detail page going forward.
Custom Buttons and Links (URL redirects) are fully supported in both the mobile web and app versions of Salesforce1 if their "Content Source" is a Visualforce page or a URL from after Spring '16.
Salesforce1 doesn't support custom buttons, but you might consider moving that button's functionality to a Publisher Action, which is supported in both the web GUI and in Salesforce1. (This is assuming your custom button is a detail button.)
Publisher Actions are clearly SFDC's preferred method for adding capabilities to a record detail page going forward.
Custom Buttons and Links (URL redirects) are fully supported in both the mobile web and app versions of Salesforce1 if their "Content Source" is a Visualforce page or a URL from after Spring '16.
- https://help.salesforce.com/articleView?id=000187793&type=1
Hope this helps.Kindly mark this as solved if the information is helpful.
Thanks,
Nagendra