BEIJING—Chinese artist Ai Weiwei vowed to keep fighting a $2.4 million tax bill after a local court rejected his challenge, an indication that the outspoken dissident has little intention of standing down in his continuing conflict with Beijing. Mr. Ai said on Friday that he plans to press his case in court over the claim. The Beijing tax bureau says the company that markets his work owes 15.22 million yuan in back taxes and fines. "We will keep appealing until the day comes that we have nothing to lose," Mr. Ai wrote on his Twitter account, adding that authorities kept him from attending the hearing. Attempts to reach Mr. Ai through his cellphone Friday were unsuccessful. The Chaoyang District Court on Friday rejected the suit after finding that the tax bureau had acted legally and properly in the investigation into Mr. Ai's company, said Mr. Ai's lawyer, Pu Zhiqiang. In an interview, Mr. Pu dismissed the decision as "shameless." Mr. Ai has said that local tax authorities have acted illegally, limiting his access to his company's financial records and to the employees who oversaw them. Repeated calls to the Chaoyang court rang unanswered on Friday. Tax charges against Mr. Ai date back to June 2011, when the artist was released following nearly three months in detention. Though Mr. Ai was detained without charge, state media said he had confessed to tax evasion and had been released after agreeing to pay back what he owed. Despite being warned by authorities to stay quiet after being let go, Mr. Ai has publicly challenged the tax case on numerous occasions. In November, after the artist announced the size of the tax bill, his supporters caused a stir by donating more than five million yuan to help him pay it, in some cases folding 100-yuan notes into paper airplanes and launching them over the wall of his home in Beijing. Many observers were surprised in May when the Chaoyang District Court agreed to hear Mr. Ai's lawsuit, which described the tax-evasion case as having been marred by numerous violations of law and procedure. Enlarge Image Reuters Authorities say Chinese dissident artist Ai Weiwei owes $2.4 million. While it is rare for a Chinese court to accept a case from a dissident, Mr. Pu on Friday rejected the notion that the mere acceptance of the case represented progress for the rule of law in the country. "I'm not willing to say this is a victory," the lawyer said. "I think this case demonstrates to the masses that the government needs to be restrained. It shows once again the shamelessness" of the authorities. Mr. Pu conceded that chances of an appeal succeeding were slim, but he said they were "not zero." The artist recently established a website, fakecase.com, where he posts materials related to the case, including a timeline. Under July 20, the timeline reads: "The verdict is in. The courts didn't accept a single argument." Reacting to the rejection of the lawsuit on Twitter, Mr. Ai appeared unsurprised by what some said was the court's failure to offer adequate justification. "This country has moved beyond needing to give reasons—it's not used to giving them and can't give them," he wrote. Write to Josh Chin at josh.chin@wsj.com A version of this article appeared July 21, 2012, on page A9 in the U.S. edition of The Wall Street Journal, with the headline: Chinese Artist Vows to Fight Latest Tax Ruling.