The documents those are required from the sponsor’s side for a K3 visa, which is being petitioned for, for the purpose of helping a spouse to migrate to the United States are as follows:

• Form 1-130 – A fully completed 1-130 form with the signatures is the first requirement for the K3 visa.
• Citizenship Evidence – A proof of your citizenship would be required to be submitted with the form. This proof could be your US birth certificate, your US passport, your certificate of citizenship, or your naturalization certificate, would be required to be submitted to the USCIS.
• 2G-325A – The biographic data sheets would be required for both the parties involved in the K3 visa petition for the migration.
• Proof of your marriage – A proof of your marriage would be required to be submitted to the USCIS. This requirement would be taken care of by your marriage certificate. In case you do not have one in that case you would have to visit your local marriage registrar and get the same done. A copy of the certificate obtained for this marriage should now be submitted.
• Documents for prior marriage nullification – In case you have had a marriage prior to your current one. Then in that case you would have to provide the relevant documents to state that the previous marriage has been nullified legally. For this you would have to submit your divorce decree or a death certificate in case of death of the previous spouse.
• Photographs – A passport size color photo of you and your spouse, which should not be older than the last 30 calendar days, needs to be given to the USCIS. On the reverse side of the photograph you should print the Alien registration number and the name of your spouse. It’s important that you should be doing this printing on the reverse side using a felt pen or a pencil only. Also you need to note that the photograph that is required to be submitted has a specification. In case you are not sure about that you can tell your photographer, about the US visa and the person would know what exactly is to be done.

As per the above mentioned, all the said documents are required to be collected and should be submitted to the USCIS along with the petition of the K3 visa. If you happen to miss out on any of these, in that case chances are that your application would be rejected.