My one yuear marriage visa expires this month and I'm preparing to get a new one. However, my passport expires next May. Any advice on whether I should get a new passport now?

Do you have time to get a new passport? You should have done this earlier. You may want to just get a single entry visa and then change passport before you travel to get a multi entry (if that is what you are talking about). If it is extension of stay believe they will extend to validity of passport and when you return with new passport transfer for full period.

Lopburi is correct, I was in a similar situation. My visa expired last September but passport was due to expire the coming August (this month). They gave me a visa extention through the last day of passport validity. After I got my new passport, I went to immigration to have the visa, re-entry permit and latest entry stamop all transferred to the new passport, which they did without charge. At which time they also extending the validity of the visa through late September (the period it would have had when I got it had my passport not been due to expire before that.) However, the re-entry permit was tran sferred only through the original date. No particular logic to that so far as I know. Transfer of the re-entry stamp is done by the re-entry counter folk not the folk who transfer the visa extension and entry stamp. I was pressed for time and didn't pursue the matter but probably could have.

So it's up to you. You can get new passport now, provided you are certain you can do so with time to spare in renewing your visa, or renew your visa now getting it approved through May and trabsfer all the stamps when you have new passport.

One point to beware of is that you may have triouble travelling to other countries when there is less than 6 months remaining in your passport validity. ...so suggest you get a new passport not later than January.