The Babygirl actress lost her father Antony in 2014 after he suffered a heart attack, while her mom Janelle died last September and she's reflected on them no longer being in her life in what would have been her mother's birthday on Thursday.
Kidman shared an old photo of her parents on Instagram and wrote: "Missing Mumma and Papa so much on what would have been her birthday today".
The 57-year-old actress previously insisted she wouldn't put a "time limit" on her grief.
Speaking in December, she told CBS Sunday Mornings, she said: "Wow, three months on, and people say to me 'Yeah, she was 84, a good life...' But that was my mum. It doesn't matter what age someone is. There is no limit on grief, you don't have to have a time limit on it, you don't have to be all better by this time.
"You're allowed to pass through in waves and people go 'Oh well, whatever', but it's my mama, my life, and I'm allowed to process and grieve in the way I want to."
The Big Little Lies star has Bella, 31, and Connor, 29, with ex-husband Tom Cruise but also has Sunday, 16, and 14-year-old Faith with spouse Keith Urban and is aware that as an "older mother" she needs to be mindful of her health after taking advice from her own mum.
She said: "And the final words my mama said to me, I was gonna get on a plane, and she said 'Maybe wait a minute, because you just need to take care of yourself, Nicky.'
"I'm doing that more, and I say that to other people in the world. Particularly, women, I think we tend not to care of ourselves. We take care of everybody else but the last person is here.
"My grandmother left me with 'be happy' and my grandmother said 'Take care of yourself.
"I'm an older mother so I wanna be around a long time for my girls, they're amazing girls and I'm lucky to have them so taking care of myself so that I can take care of them.
"I would like to be around for a long time. Who knows? I don't get to choose that."
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