 <p>Try :</p> <pre><code>NSMutableArray *first=[NSMutableArray arrayWithArray:@[@"1",@"2",@"3",@"4",@"5",@"6"]]; NSMutableArray *second=[NSMutableArray arrayWithArray:@[@"2",@"4",@"6",@"8",@"0",@"12"]]; for (id obj in second) { if (![first containsObject:obj]) { [first addObject:obj]; } } NSLog(@"%@",first); </code></pre> <hr> <p>EDIT: </p> <pre><code>NSMutableArray *first=[NSMutableArray arrayWithArray:@[@"1",@"2",@"3",@"4",@"5",@"6"]]; NSMutableArray *second=[NSMutableArray arrayWithArray:@[@"2",@"4",@"6",@"8",@"0",@"12"]]; NSMutableOrderedSet *firstSet=[NSMutableOrderedSet orderedSetWithArray:first]; NSOrderedSet *secondSet=[NSOrderedSet orderedSetWithArray:second]; [firstSet unionOrderedSet:secondSet]; first=[[firstSet array] mutableCopy]; NSLog(@"%@",first); </code></pre> <p>*<em>Credit goes to Mark Kryzhanouski</em></p>