Livestock and dairy farmers in particular have been badly hit by falling prices on world markets.
They have been hit by tough competition between supermarkets as well as a Russian embargo on EU food imports.
The BBC`s Hugh Schofield in Paris says it was a noisy, eye-catching, disruptive protest from the farmers in the centre of the capital.
The protesters want to put maximum possible pressure on President Francois Hollande`s Socialist government, which has already given way once, just six weeks ago, with a package of debt relief worth €600m ($674m; £440m), our correspondent says.
But the farmers say that they need much more, arguing that French agriculture is on the verge of collapse.
Their tractors, spray-painted with "Anger`" or "Enough Bureaucracy", trundled on Thursday morning along major roads in the capital.
They came from all parts of the country to take part in the demonstration.
Although key roads were blocked, many commuters appeared to have taken public transport, as advised by police.
Dairy farmer Maxime Pilorget told French TV that he was losing money hand over fist because the daily income he was receiving for his cows` milk was far less than the cost of producing it.
"Morally, the hardest thing is to be unable to make a living from my work," he said.
Dairy farmers in particular have seen incomes collapse because of over-production on the world market. Correspondents say they have also been adversely affected by changing dietary habits and slowing Chinese demand.
Grain farmer Pierre Bot, from Vauhallan south of Paris, told AP news agency that while "it`s not popular to annoy all the people on their way to work" such a tactic was necessary for farmers to make themselves heard.
Pork farmers, meanwhile, face competition from the vast piggeries of Denmark and Germany, where production costs are much lower.
Our correspondent says that French agriculture faces something of an existential crisis as it struggles to adapt - after decades of protection - to a globalised ultra-competitive world.
Earlier in the summer protesting farmers throughout the country dumped manure in cities, blocked access to roads and stopped tourists from travelling to the popular Mont St-Michel island in northern France.
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