In the apple document, I can see that there's a way to convert from UTF8 string to ASCII string like this NSData *asciiData = [theString dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]; NSString *asciiString = [[NSString alloc] initWithData:asciiData encoding:NSASCIIStringEncoding]; But my app requires a TIS-620 string to post to a site so I try to do the same thing NSData *asciiData = [newPost.header dataUsingEncoding:kCFStringEncodingMacThai allowLossyConversion:YES]; NSString *asciiString = [[NSString alloc] initWithData:asciiData encoding:kCFStringEncodingMacThai]; NSLog(@"%@", asciiString); The output I got is like this ???????????. Does anyone know how to convert the NSString to TIS-620 properly? Thanks so much.