Google Apps Script for converting Excel (.xls or .xlsx) file to Google Spreadsheet. Drive API must be enabled in your script's Advanced Google Services and in Developers Console for the script to work (see https://developers.google.com/apps-script/guides/services/advanced#enabling_advanced_services for details).

convertExcel2Sheets

/**
 * Convert Excel file to Sheets
 * @param {Blob} excelFile The Excel file blob data; Required
 * @param {String} filename File name on uploading drive; Required
 * @param {Array} arrParents Array of folder ids to put converted file in; Optional, will default to Drive root folder
 * @return {Spreadsheet} Converted Google Spreadsheet instance
 **/
function convertExcel2Sheets(excelFile, filename, arrParents) {
  
  var parents  = arrParents || []; // check if optional arrParents argument was provided, default to empty array if not
  if ( !parents.isArray ) parents = []; // make sure parents is an array, reset to empty array if not
  
  // Parameters for Drive API Simple Upload request (see https://developers.google.com/drive/web/manage-uploads#simple)
  var uploadParams = {
    method:'post',
    contentType: 'application/vnd.ms-excel', // works for both .xls and .xlsx files
    contentLength: excelFile.getBytes().length,
    headers: {'Authorization': 'Bearer ' + ScriptApp.getOAuthToken()},
    payload: excelFile.getBytes()
  };
  
  // Upload file to Drive root folder and convert to Sheets
  var uploadResponse = UrlFetchApp.fetch('https://www.googleapis.com/upload/drive/v2/files/?uploadType=media&convert=true', uploadParams);
    
  // Parse upload&convert response data (need this to be able to get id of converted sheet)
  var fileDataResponse = JSON.parse(uploadResponse.getContentText());

  // Create payload (body) data for updating converted file's name and parent folder(s)
  var payloadData = {
    title: filename, 
    parents: []
  };
  if ( parents.length ) { // Add provided parent folder(s) id(s) to payloadData, if any
    for ( var i=0; i<parents.length; i++ ) {
      try {
        var folder = DriveApp.getFolderById(parents[i]); // check that this folder id exists in drive and user can write to it
        payloadData.parents.push({id: parents[i]});
      }
      catch(e){} // fail silently if no such folder id exists in Drive
    }
  }
  // Parameters for Drive API File Update request (see https://developers.google.com/drive/v2/reference/files/update)
  var updateParams = {
    method:'put',
    headers: {'Authorization': 'Bearer ' + ScriptApp.getOAuthToken()},
    contentType: 'application/json',
    payload: JSON.stringify(payloadData)
  };
  
  // Update metadata (filename and parent folder(s)) of converted sheet
  UrlFetchApp.fetch('https://www.googleapis.com/drive/v2/files/'+fileDataResponse.id, updateParams);
  
  return SpreadsheetApp.openById(fileDataResponse.id);
}

/**
 * Sample use of convertExcel2Sheets() for testing
 **/
 function testConvertExcel2Sheets() {
  var xlsId = "0B9**************OFE"; // ID of Excel file to convert
  var xlsFile = DriveApp.getFileById(xlsId); // File instance of Excel file
  var xlsBlob = xlsFile.getBlob(); // Blob source of Excel file for conversion
  var xlsFilename = xlsFile.getName(); // File name to give to converted file; defaults to same as source file
  var destFolders = []; // array of IDs of Drive folders to put converted file in; empty array = root folder
  var ss = convertExcel2Sheets(xlsBlob, xlsFilename, destFolders);
  Logger.log(ss.getId());
}