Stewart, who is roughly halfway through a five-month sentence for lying about a stock sale, urged fans to think about the women she has met in prison who are "devoid of care, devoid of love, devoid of family."
She suggested Americans should push for reforms in federal sentencing guidelines for nonviolent first-time offenders and particularly for drug offenders, who she said would be better served by rehabilitation than prison.
Stewart, who built a billion-dollar empire in homemaking, reported that her job at the federal prison camp in Alderson, W.Va., has been cleaning, including sweeping, vacuuming and raking leaves.
"I have had time to think, time to write, time to exercise, time to not eat the bad food, and time to walk and contemplate the future," she said.
Earlier this month, her company, Martha Stewart Living Omnimedia, announced Stewart would host a daytime talk show with a studio audience beginning this fall.
The company has been working with reality TV pioneer Mark Burnett, and shares of the media company have soared since Stewart reported to prison - although they have fallen back somewhat in recent weeks.
Stewart is due to be released in early March from Alderson, then must spend five months confined to her home in Bedford, N.Y. The television show is scheduled to air after the five months of house arrest end.
Stewart and her former stockbroker, Peter Bacanovic, were convicted in March of lying about why Stewart unloaded shares of ImClone Systems Inc. stock in 2001, just before the price plunged. Both are appealing.
Shares of Martha Stewart Living Omnimedia were up 86 cents, or more than 3 percent, at $28.10 in midday trading Wednesday on the New York Stock Exchange. They traded below $9 before her sentencing in July.
By Erin McClam