forgot sys password in oracle 11g.

Hi,

Log on to your Windows server as a member of the Administrators group or a member of the ORA_DBA group.

Try the below steps
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\NIIT>set oracle_sid=orcl

C:\Users\NIIT>sqlplus /nolog

SQL*Plus: Release 11.2.0.1.0 Production on Mon Jan 30 16:27:11 2017

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

SQL> connect /as sysdba
Connected.
SQL> alter user sys identified by admin;

User altered.

SQL> conn
Enter user-name: sys as sysdba
Enter password:
Connected.
SQL> show user

USER is "SYS"