Remember that your img is not really a DOM element but a javascript expression.
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This is a JSX attribute expression. Put curly braces around the src string expression and it will work. See http://facebook.github.io/react/docs/jsx-in-depth.html#attribute-expressions
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In javascript, the class attribute is reference using className. See the note in this section: http://facebook.github.io/react/docs/jsx-in-depth.html#react-composite-components
/** @jsx React.DOM */ var Hello = React.createClass({ render: function() { return <div><img src={'http://placehold.it/400x20&text=slide1'} alt="boohoo" className="img-responsive"/><span>Hello {this.props.name}</span></div>; } }); React.renderComponent(<Hello name="World" />, document.body);